“This is who Donald Trump is,” wrote the 13, all “lifelong Republicans,” according to the letter. “Donald Trump’s disdain for the American military and admiration for dictators like Hitler is rooted in his desire for absolute, unchecked power.”

The letter did not describe any of the former officials hearing Mr. Trump speaking glowingly of Hitler, the Nazi dictator who presided over the systematic slaughter of six million Jews and millions of others.

But the letter said its signers had “witnessed, up close and personal, how Donald Trump operates and what he is capable of.”

“The American people deserve a leader who won’t threaten to turn armed troops against them, won’t put his quest for power above their needs, and doesn’t idealize the likes of Adolf Hitler,” the letter said.

Mr. Kelly described Mr. Trump’s appreciation of history as limited, and he recalled attempting to explain to the president why it was problematic to praise Hitler. Still, Mr. Kelly said, Mr. Trump continued to make positive comments about Hitler.

In this year’s election, Mr. Trump has described Democrats, some by name, as the “enemy from within” and has contemplated deploying the National Guard to address the threat he claims they could pose.

The letter, organized on Wednesday after Mr. Kelly’s comments were published in The Times on Tuesday, was signed by several outspoken Harris supporters, including two who gave speeches at the Democratic National Convention: Stephanie Grisham, a former Trump White House press secretary, and Olivia Troye, who was an adviser to Mr. Trump’s vice president, Mike Pence.

Other signers included Anthony Scaramucci, who had a memorable 10-day run as communications director in the Trump White House; Brooke Vosburgh Alexander, who was a top aide in the Commerce Department; Alyssa Farah Griffin, who served as Mr. Pence’s press secretary; Mark Harvey and Peter Jennison, who worked on the National Security Council; Sarah Matthews, a former deputy White House press secretary; and Robert Riley, who was the U.S. ambassador to Micronesia.

Three former Homeland Security Department officials also signed the letter: Kevin Carroll, Elizabeth Neumann and Sofia Kinzinger, who is married to former Representative Adam Kinzinger of Illinois, one of the most vocal Republican opponents of Mr. Trump after the Jan. 6, 2021, attack on the U.S. Capitol.

“For the good of our country, our democracy, and our Constitution, we are asking you to listen closely and carefully to General Kelly’s warning,” they wrote.

The first reference came in an interview with the conservative radio host Hugh Hewitt. “You’re either going to have to pardon yourself or you’re going to have to fire Jack Smith,” Mr. Hewitt said. “Which one will you do?”

“It’s so easy,” Mr. Trump responded. “I would fire him within two seconds.”

In the other interview, on WABC, a conservative radio station in New York, he was using the alarmist language with which he describes undocumented immigrants as part of his hard-line immigration policies and repeating his pledge to conduct mass deportations when he pivoted to Mr. Smith.

“You have to get the killers, the murders, and mentally deranged, you have to get them out,” Mr. Trump said. “And we should throw Jack Smith out with them, the mentally deranged people. Jack Smith should be considered mentally deranged and he should be thrown out of the country.”

It was not immediately clear what legal mechanism, if any, might allow such an action. A spokesman for Mr. Smith declined to comment.

Mr. Trump’s comments added to his promises of revenge on his political enemies, whom he has pledged to prosecute and investigate. He has escalated his threats against those he considers adversaries, including raising the possibility of deploying the military or the National Guard against “the enemy from within,” a catchall term he has used for years to refer to the left. He recently named two top Democratic representatives from California, Adam Schiff and Nancy Pelosi, the former House speaker, as figures he considered under that label.

Though Mr. Trump frequently portrays himself as the victim of politically motivated prosecutions, during his presidency he repeatedly pushed the Justice Department to investigate some people he considered foes, and some then came under various forms of federal government pressure.

Mr. Trump and his allies have developed a legal framework to allow Mr. Trump to subvert the Justice Department’s independence from the president, part of a series of plans for a potential second term that would upend key areas of American governance, democracy and the rule of law.

The group’s paperwork was signed by May Mailman, who worked in the Trump White House and who is now the director of the Independent Women’s Law Center. She did not immediately respond to a request for comment Friday.

Ms. Mailman posted the ads online and said they featured a “suburban mom” who had never voted for Trump before but was backing him now because he has said he opposes a national abortion ban.

The ad she posted features a woman in a pink sweater sitting in a chair in a living room saying her life was better under Mr. Trump. She says that “freedom to choose is also important to me” and that she is voting for Mr. Trump, citing his support for exceptions to abortion restrictions in cases of rape, incest and risk to the life of the mother.

“His position is my position,” the woman says.

Mr. Trump has taken credit for overturning Roe v. Wade, which returned the issue of abortion to states, many of which have banned the procedure.

He has since worked to improve his standing with voters on the abortion issue, which polls show remains a significant advantage for Vice President Kamala Harris.

The RBG PAC’s website features two large pictures of Mr. Trump and Ms. Ginsburg and the words: “Great Minds Think Alike.”

The group’s use of Ms. Ginsburg’s name and likeness is particularly brash given that Mr. Trump, as president, appointed the Supreme Court justice who succeeded her. That appointee, Justice Amy Coney Barrett, voted with the majority to overturn Roe v. Wade.

It is common at the end of a presidential campaign for so-called “pop-up” groups to begin spending large amounts of money after the last financial disclosure deadline. Any groups that were active by Oct. 16, the last day of the last filing period before Election Day, would have been required to disclose donors or vendors working with the group.

RGB PAC filed its paperwork on Oct. 16.

“While it is permissible to game the system in this way under the FEC reporting rules that were written in the 1970s, in my experience only a campaign that believes that it is losing resorts to this tactic,” said Brett Kappel, a Democratic campaign-finance lawyer at the firm Harmon Curran.

The amount of money that the super PAC is spending suggests that it took in considerable resources in just the last week. It reported $17.3 million in digital media spending, $1.6 million on text measures and $1 million for printing and postage.

There are a number of megadonors who have been pouring money into the 2024 race, none more so at this stage than Elon Musk, the world’s richest man and the co-founder of Tesla, who has spend $119 million as of mid-October.

During an appearance on CNN this month, Ms. Mailman defended some of Mr. Musk’s tactics, including the offer to pay swing-state voters as much as $1 million to sign a petition. The Department of Justice has signaled that it could find Mr. Musk’s offer illegal, sending his super PAC a “warning letter” this week.

“There is something to super PACs using their money smarter and not just flooding the airwaves,” Ms. Mailman said on CNN.

She continued, “Getting people’s eyeballs, getting people to pay attention to this election is, I think, not just going to be the standard advertisements that we see. I think creativity is warranted in elections.”

With less than two weeks until Election Day, House Democrats’ campaign arm has sued the Federal Election Commission for failing to stop the Republicans and are seeking a ruling to either bar the practice or clear the way to use it themselves.

A hearing on the matter is set for Monday, and both parties expect a ruling as soon as Tuesday, either blocking or allowing the practice in the critical last stretch before Election Day.

Here’s what to know:

Democrats have been dominating Republicans in fund-raising in key Senate races.

Continuing a recent trend, Democratic Senate candidates have been trouncing their Republican rivals in fund-raising battles in pivotal races across the country.

In Ohio, Senator Sherrod Brown has raised about four times as much money as his Republican challenger, Bernie Moreno. In Montana, Senator Jon Tester has raised about three times as much as Tim Sheehy. And in Arizona, Representative Ruben Gallego has raised more than twice as much as Kari Lake.

Races in Pennsylvania, Wisconsin and Nevada also show large fund-raising leads for Democrats.

Republicans are exploiting a legal loophole to try to close the gap.

Congress has placed strict limits on contributions from national party committees to individual candidates. Those have led to strict requirements governing when and how national parties can cover the cost of campaign advertisements for individual candidates. For so-called hybrid ads, they must split the cost with the candidate, and no more than half the ad can be about a specific race; at least as much time must be spent advocating for general candidates of the party.

But the National Republican Senatorial Committee is skirting those rules and running tens of millions in ads for individual candidates by categorizing them as joint fund-raising appeals. Those are subject to a different set of regulations that allow coordination and place no limits on content beyond that it must include a solicitation.

They are doing so by simply adding a “donate now” appeal in the last few seconds of the ad with a QR code that links to a donation page for a joint fund-raising committee established between the committee and the Republican candidate.

Not only does the technique allow national Republicans to ignore the content restrictions of a hybrid ad, it also allows them to take advantage of a lower television advertising rate available to candidates.

Republicans began testing the strategy in Montana in July with an ad for Mr. Sheehy. After he discusses his military service, the ad ends with the phrase, “Join my team, give now.”

Republicans have begun running similar ads in Maryland, Arizona, Wisconsin, Michigan and Nebraska to help bolster their candidates who were lagging in fund-raising.

Since they began using the strategy, Republicans have noticed an uptick in polls for their candidates in key Senate races, they say.

The strategy has prompted outrage from Democrats, even though they pioneered it.

Democrats argue that Republicans are making a mockery of campaign finance laws, because their so-called joint fund-raising appeals are focused almost entirely on advocating a candidate’s election and are coordinated with the candidate.

“This spending far exceeds the limits set forth in federal law and is illegal,” lawyers for House Democrats wrote, adding, “As such, the N.R.S.C. and Republican candidates should be on the hook for large fines and penalties.”

The Democrats fault the F.E.C. for failing to render an opinion as to whether the Republicans’ practices are legal. But the commission, which is charged with enforcing federal campaign finance laws, deadlocked 3-3 along party lines, as it often does, and could not issue a decision on the matter.

That left House Democrats “between a rock and a hard place on the eve of the November election,” their lawyers wrote. “It may adhere to federal law, as it best understands it, but in doing so must sit on its hands while Republicans invest tens of millions of dollars into arguably illegal television advertisements. Alternatively, D.C.C.C. may mimic this newfound tactic, but at the risk of exposing itself and its participating candidate committees to future enforcement — including felony criminal prosecutions brought by the U.S. Department of Justice.”

Republicans argue they are merely using a practice that Democrats pioneered and embraced.

The advertising strategy Republicans are using “is not a new phenomenon,” their lawyers said, citing its use during the presidential campaigns of President Barack Obama, Secretary of State Hillary Clinton and Vice President Joseph R. Biden Jr.

Moreover, the Republicans note, House Democrats are complaining about a tactic that Senate Democrats have also used for their candidates during this campaign cycle.

“The N.R.S.C. would be injured if it is forced to change its joint fund-raising ads,” Jason Thielman, the group’s executive director, wrote in an affidavit, noting that it would have to make several late changes and incur substantial costs.

Democrats concede that some on their side have used joint fund-raising committees for Senate candidates, but they say they are doing so only online and argue that they are complying with the spirit of the hybrid ad rules.

Ms. Harris’s rally in Houston will focus on the strict abortion ban enacted in Texas after the overturning of Roe v. Wade, and is meant to offer a warning about the potential spread of such restrictions to voters in faraway states who will soon decide this year’s presidential election.

In short, the Harris team wants to put what happens deep in the heart of Texas on display for the whole country to see.

“If it takes Vice President Harris to elevate the voices of women in Houston so they are heard in Madison and Kalamazoo and Pittsburgh, that’s what we’re going to do,” said Trey Martinez Fischer, the Democratic leader in the Texas State House.

Just about everything related to Ms. Harris’s Houston trip is engineered to create news that will reach voters in the battleground states. Before the rally with Beyoncé and Mr. Nelson, she is scheduled to record a podcast interview with the popular podcaster Brené Brown, a University of Houston professor and vulnerability researcher who has an audience of millions that skews heavily female.

Ms. Harris is following a path traveled recently by former President Donald J. Trump, who held campaign events in Aurora, Colo., and Coachella, Calif., and is set to appear on Sunday at Madison Square Garden in New York. The Trump campaign has not invested in and does not expect to win any of those states, just as Ms. Harris is not pretending she has a chance to win Texas.

Mr. Trump is planning his own Texas sojourn on Friday, heading to Austin to record Joe Rogan’s podcast. He is also scheduled to appear with Senator Ted Cruz, the Republican who is being challenged by Representative Colin Allred.

It is the latest evidence that in modern presidential campaigns, viral content in social media feeds is just as desirable as a segment on local TV news in battleground states. Harris aides calculate that those stations will probably end up showing footage of Ms. Harris and the music stars anyway.

Both Ms. Harris and Mr. Trump have dispensed with what used to be a flurry of interviews that presidential nominees gave to local television stations. Barack Obama, during his campaigns, and Joseph R. Biden Jr. four years ago often stacked several local TV interviews in a row to ensure that they had a presence in markets even while traveling elsewhere.

Ms. Harris has held a few local interviews, with outlets including Philadelphia and Atlanta television last month, but she has generally focused on platforms with national audiences. Her team believes this makes her appearances more likely to be aggregated and shared beyond the market where an interview aired.

When she appeared this month on two popular podcasts, “Call Her Daddy” and “All the Smoke,” 26 percent of likely voters heard her speak, according to a poll released this week by USA Today and Suffolk University.

Then there is the matter of making a national argument about abortion rights, with Texas as ground zero. Ms. Harris has used the state’s near-total abortion ban as a cautionary tale in her stump speeches, reminding audiences that physicians face a potential death penalty for providing abortion care that was legal before the Supreme Court’s decision in Dobbs v. Jackson Women’s Health Organization two years ago.

The campaign has used Kate Cox and Amanda Zurawski, Texas women who became high-profile abortion rights activists after they sued Texas over its restrictions, as prominent surrogates who have traveled to other states. Ms. Zurawski, who addressed the Democratic National Convention, is among the speakers expected to address the rally on Friday.

“There’s no state in the country that is as clear of an example of the devastation millions of women are experiencing post-Dobbs than Texas,” said Skye Perryman, a Texas native who is the president of Democracy Forward, a legal group that has been involved in the Texas abortion lawsuits. “These are issues for all people in the country, not just for those who may live in a state that gets particular attention this time of year.”

While Democrats have dreamed of making Texas competitive in presidential elections, the political realities and financial costs of competing in a state with 20 media markets have led the party to invest its resources elsewhere.

No Democrat has won a statewide election in Texas since 1994. Ms. Harris’s Houston rally appears to be the first for a Democratic presidential nominee in Texas this late in a campaign since President Bill Clinton went to San Antonio in the final days before the 1996 election.

“It was a different state,” said Garry Mauro, who ran Mr. Clinton’s campaigns in Texas and stood onstage with Mr. Clinton in front of the Alamo on Nov. 2, 1996, three days before Election Day. Mr. Mauro, a former land commissioner of the state, was also among the last Democratic officials elected statewide before Republicans began asserting their dominance.

Coming to Houston brings Ms. Harris to Harris County, the most populous county in Texas and the beating heart of its Democratic base.

Huge turnout in the county, home to 2.7 million registered voters, is an absolute must for Democrats for them to have any hope of overcoming the significant advantage that Republicans have had in rural areas of the state. The Harris County Democratic Party has calculated that around 500,000 likely Democrats in the county did not vote in 2020.

Some Harris aides briefly argued this week, before it was revealed that Beyoncé would appear at the Friday rally, that her visit was meant to help Mr. Allred in his Senate race.

But she has not traveled to Ohio or Montana to aid their vulnerable Democratic senators. And top Texas Democrats seemed unaware of Ms. Harris’s Houston plans before they were revealed publicly.

The visit could potentially backfire on Mr. Allred, who has worked to put some distance between himself and Ms. Harris. Republicans were all too happy to embrace the visit.

“Colin Allred is Kamala Harris,” the Cruz campaign blasted in an email as soon as the event was announced.

“He didn’t even know why the hell he got it,” said Mr. Trump, who had spent years trying to undermine the legitimacy of the country’s first Black president with baseless claims about his citizenship.

Mr. Trump suggested he was more deserving of the honor than his predecessor in the White House, saying his full name, Barack Hussein Obama, twice for emphasis.

“I got elected in a much bigger, better, crazier election, but they gave him the Nobel Prize,” he said.

With 12 days until Election Day, Mr. Trump sharpened his attacks on Ms. Harris over immigration on Thursday, using the speech in Nevada and another in Arizona to gin up support for his plans to begin the largest mass deportation in U.S. history if elected.

“We’re like a garbage can for the world,” he said during a speech at Arizona State University, where he repeatedly vilified migrants.

Mr. Trump clung to that theme a few hours later at a rally held by Turning Point PAC, a group aligned with him, saying that Democrats had allowed an “invasion” of illegal immigrants. He said their border policies were the result of stupidity, hatred for the country and a desire to get illegal immigrants to vote for them.

Mr. Trump’s message followed the typical contours of his often-rambling speeches, bringing up lingering grievances and casting the prospect of Ms. Harris’s winning the election as a catastrophe for the country.

“If Kamala gets four more years, she will obliterate our economy, kill millions of jobs — kill thousands of people, too, by the way — and destroy your family finances probably forever,” Mr. Trump told the crowd.

In between the two rallies, the former president visited a Cuban restaurant and bakery about 10 minutes off the Las Vegas Strip with Senator Marco Rubio, the Florida Republican who grew up in Las Vegas and whose parents immigrated to the U.S. from Cuba. Mr. Rubio joined him at all three of his stops on Thursday, part of an apparent effort by Mr. Trump to cultivate support from Latino voters.

From the onset of his remarks in Las Vegas, where he was introduced by former Representative Tulsi Gabbard, an estranged former Democrat who is now a Republican, Mr. Trump acknowledged watching Ms. Harris’s rally in Georgia.

He told his audience that Ms. Harris had “bombed” during the event and falsely claimed that he was far ahead of her in the polls in several battleground states that will most likely decide the election.

“She’s actually imploding, if you take a look,” he said.

He also played a clip from her appearance one night earlier on a CNN town hall in Pennsylvania, a forum that he had declined to participate in. In the clip, Ms. Harris was asked by Anderson Cooper whether she had made any mistakes: she said of course she had as a parent and was perhaps at times overly deliberative on difficult issues. The crowd jeered and one person in the audience shouted an obscenity.

Combined with their main allied super PACs, the Harris and Trump operations spent an extraordinary half-billion dollars in just 16 days. The Harris and Trump campaigns combined to spend about $265 million during that period, and the main pro-Harris super PAC, plus the four main pro-Trump super PACs, spent roughly an additional $260 million.

The reports offered a close-to-current view of the financial fortunes of Ms. Harris and Mr. Trump, capturing activity from Oct. 1 through Oct. 16. They are the last filings with the Federal Election Commission before Election Day.

Here is a look at what the new finance reports can tell us about the state of the race.

Heavy spending, but a huge Harris cash advantage

The point of all the money, of course is to spend it. And spend it they have.

Ms. Harris spent $166 million during that 16-day period, almost equal to what she spent in the entire month of August; $130 million of that was spent on media.

Alongside her allied committees, she raised $182.6 million in early October, according to a New York Times analysis of campaign-finance reports. She and President Biden together have raised $1.8 billion with the party.

Mr. Trump and his allied committees raised about half Ms. Harris’s total, $92.1 million, during the 16-day window. He crossed the $1 billion threshold in the amount he has raised with the party since announcing his run for president in November 2022, according to The Times’s analysis.

The money flowed out rapidly, though. Mr. Trump’s principal committee spent $100 million in the 16-day period, more than he spent in June, July and August combined. He spent $88 million of that on advertising.

He entered the second half of October with $36.2 million on hand. Ms. Harris had three times that — $119 million — leaving her in a much better financial position for the final three weeks of the election.

Democrats have built a bigger organization in their parties, too. The Republican National Committee, as of Oct. 16, had $48 million on hand. It transferred $23.8 million to state parties in battlegrounds and paid salaries to about 355 people during that period. The Democratic National Committee had about $30 million on hand after transferring $44 million to state parties and paying about 740 people.

The biggest Democratic group’s biggest donor? Unknown.

The largest Democratic super PAC, Future Forward, prioritizes late ad purchases, and much of the money it has raised came late in the cycle. Just on Wednesday, for instance, the group disclosed a mammoth $82 million ad purchase.

The group raised $89 million in the first half of October, or almost $6 million a day. Dustin Moskovitz, a co-founder of Facebook, chipped in $25 million during the period, on top of his prior $13 million, making him the largest disclosed donor to the group in the cycle.

But the largest actual donor remains a mystery. During early October, $40 million of the $89 million raised came from the super PAC’s allied dark-money group, whose donors remain secret, continuing a trend of secrecy that has defined the group’s rise.

Elon Musk’s Trump budget: $119 million

Over just 16 days, Elon Musk spent $57 million to support Republicans.

Mr. Musk, the world’s richest person, put an additional $43.6 million into his super PAC, America PAC, between Oct. 1 and Oct. 16, increasing his total pro-Trump spending to a staggering $119 million. Mr. Musk is now the second biggest pro-Trump donor, climbing above Miriam Adelson, the Las Vegas casino magnate, but below Timothy Mellon, heir to the Mellon banking fortune.

Mr. Musk also disclosed a $10 million check to the Senate Leadership Fund, the main super PAC for Senate Republicans, which is led by allies of Senator Mitch McConnell. That donation was Mr. Musk’s largest by far in his career, outside of the checks he cut to his own super PAC this year.

Mr. Musk gave $825,000 to a super PAC in support of a political ally, Representative Tony Gonzales of Texas. Mr. Musk also contributed $2,339,600 to the Sentinel Action Fund super PAC, which, like Mr. Musk’s organization, is doing voter canvassing in Pennsylvania. The leader of that group, Jessica Anderson, suggested on social media that Mr. Musk’s precise amount was to close the group’s exact funding gap in Pennsylvania. “Thank you @elonmusk for catching the early vote/ absentee vision!”

Other donors cutting checks in early October to pro-Trump super PACs included Dick and Liz Uihlein, leaders of the ULine shipping supply company ($9.5 million); Jan Koum, a WhatsApp co-founder ($5 million); Diane Hendricks, a roofing magnate ($5 million); Ron Cameron, a poultry company C.E.O. ($2 million); the venture capitalist Marc Andreessen ($2 million); and Safra Catz, the Oracle C.E.O. ($1 million).

Mr. Andreesen, who runs a prominent Silicon Valley firm with Ben Horowitz, famously split earlier this fall on the presidential race. Mr. Andreesen made his donation to support Mr. Trump’s group on the same day, Oct. 7, that Mr. Horowitz donated $2.5 million to a pro-Harris super PAC.

Albert Sun contributed reporting.

“I’ve watched him, from the Central Park Five to Project 2025,” Mr. Perry said of Mr. Trump, before formally endorsing Ms. Harris, “and what I realized is that in this Donald Trump America, there is no dream that looks like me.”

Mr. Perry’s speech stood in sharp contrast to the lighter talking points about voting and community organizing that have often defined Democratic events this election cycle. He has donated millions to local causes in Atlanta, such as paying for students’ college tuition and purchasing homes for low-income people, and he said that Ms. Harris’s promises to lower health care costs made her “a candidate that I can stand with.”

Onstage on Thursday night, Mr. Perry discussed a litany of policies around immigration, health care and housing. He also marked a contrast between his life story and that of Mr. Trump, who he said had “a father who had millions of dollars” and could not understand the struggles of lower- and working-class Black voters.

“If you are like me,” said Mr. Perry, who was once homeless in Atlanta, “I worked my ass off to buy my first house, to build my business and take care of my family.”

Still, Mr. Perry’s most pointed argument perhaps came through his most recognizable character, Madea, a no-nonsense maternal figure whom he has portrayed in some of his most popular movies. Referring to Mr. Trump’s statement at the presidential debate last month that he has “concepts of a plan” for health care policy, he invoked one of Madea’s catchphrases: “What the hell?”

Mr. Perry’s remarks, which he said he was delivering just after casting his ballot for Ms. Harris, underscore the urgency that Georgia Democrats are feeling in the final weeks of the presidential campaign. Over two million voters have already cast ballots in the state, more than the early voting record of roughly 1.8 million, set around this time in 2020. Democrats are especially eager to increase enthusiasm in the Atlanta metropolitan area, the deep-blue engine of the battleground state. Mr. Perry encouraged those in the crowd to vote, reminding them of Joseph R. Biden Jr.’s razor-thin margin of victory in 2024.

“I stand here, full-throated, with my full chest, begging you, imploring you: Let’s get out and make Kamala Harris the 47th president of the United States,” he said.

In addition to Mr. Perry, the filmmaker Spike Lee and the actor Samuel L. Jackson also spoke at Ms. Harris’s rally, and Bruce Springsteen performed. The vice president has attracted considerable star power during her campaign. She has also appeared with Stevie Wonder, Lizzo and Usher, and Beyoncé is set to appear at a rally for her in Texas on Friday.

Morgan Ackley, Mr. Trump’s spokeswoman in Georgia, criticized Thursday’s event in a statement, saying that “a free concert and an Obama visit isn’t going to convince Georgians to vote for another four years of open borders, rising prices and disaster at home and abroad.” Mr. Obama also spoke at Ms. Harris’s rally.

In his remarks, Mr. Perry celebrated the country’s diversity. “We are all shapes, sizes and colors, but we are one,” he said. “It was so important for me to stand with a candidate who understands that we, as America, we are a quilt. And I could never stand with a candidate who wants us to be a sheet.”

Yet Ms. Adelson, a physician and a conservative megadonor, and her operatives have been eager to keep Mr. Trump on television in the battleground states of Wisconsin and Michigan, especially given that he is being outspent by Vice President Kamala Harris and her allies. So other donors have said that beginning in early October, Ms. Adelson has been soliciting other billionaires to help bridge the gap to keep the group on the air through Election Day.

“We had an initial $100 million,” said Dave Carney, a senior adviser to the group. “We’re trying to raise more, and Dr. Adelson has been a fund-raising star getting more people on board.”

Super PACs formed by a single rich donor can struggle to raise outside money as fellow billionaires wonder why the patron won’t foot the whole bill. Ms. Adelson has raised over $10 million for her super PAC over the last few weeks, a spokesman for her said. Supporters of the group who will be made public in a Thursday filing with the Federal Election Commission include the conservative billionaires Liz Uihlein, Ronnie Cameron and Diane Hendricks, who gave $3 million, $2 million and $1 million, respectively. Mr. Carney said the group now had over 100 donors.

Ms. Adelson has also been collaborating on raising money for another pro-Trump super PAC, MAGA Inc. On Thursday, one person who considers Ms. Adelson to be a mentor — Jan Koum, the billionaire co-founder of WhatsApp — disclosed having given a $5 million check to MAGA Inc. earlier this month.

Ms. Adelson was planning to host an event for MAGA Inc. in Las Vegas earlier this month that would have featured Dana White of the Ultimate Fighting Championship and Mr. Trump, but the groups called off the event because it came too close to the Jewish holiday of Yom Kippur. Some donors had been asked for $1 million contributions in connection with that event.

Ms. Adelson has emerged as one of Mr. Trump’s strongest supporters, even though Mr. Trump has not always seemed especially appreciative. Mr. Trump told associates earlier this year that he expected Ms. Adelson to donate an extraordinary $250 million to back him — an expectation that it appears she will not meet.