WASHINGTON — A looming battle among Senate Republicans over whom to pick as their next majority leader is turning into an early test of how much power President-elect Donald Trump's MAGA movement will exert in his second term.

The three-way fight to replace outgoing Senate Republican leader Mitch McConnell of Kentucky, pits Minority Whip John Thune of South Dakota against John Cornyn of Texas, a former McConnell deputy, and underdog candidate Rick Scott of Florida.

The battle will gauge the staying power of long-serving senior Republicans grounded in an institutionalist view of the Senate, like Thune and Cornyn, against an emboldened pro-Trump wing looking to smash any vestiges of the old GOP as he returns to power.

Scott, who's seeking to claim the latter mantle, said in an interview Monday that he'll push “the Trump agenda” if he's elected.

“I talk to all my colleagues, and they are clear what they want and know we need to change. They want to be treated as equals, want to be part of a team. They know I have a great relationship with Trump and the speaker of the House, and I am a business guy. And I will get the Trump agenda done,” Scott said.

MAGA influencers online have started an online pressure campaign to sink the current and former McConnell deputies — and boost Scott — ahead of a candidate forum Tuesday and an expected closed-door election Wednesday.

Right-wing commentator Tucker Carlson said Scott is the “only candidate who agrees with Donald Trump” and claimed the two other contenders “hate Trump and what he ran on.” (Thune and Cornyn have been critical of Trump in the past, but both endorsed him this year.)

Billionaire Trump benefactor Elon Musk also endorsed Scott, saying Monday, “The new Senate Majority Leader must respond to the will of the people.”

Rep. Marjorie Taylor Greene, R-Ga., one of Trump's top allies on the Hill, encouraged senators to elect Scott. “The Republican conference should choose a leader who represents the People, not the same good ole’ boy way it’s been done for decades,” Greene said on X.

But it’s far from clear that the campaign will succeed. The Senate is a famously insular body that is relatively detached from populist fervor, giving members six-year terms and usually operating on seniority. It would be unusual for Scott to leapfrog two colleagues who have served much longer, cultivated deeper relationships and have each paid their dues in pursuit of the job.

Most importantly, the election will be held by secret ballot. Unlike votes on legislation and nominations — as well as the vote for speaker of the House — votes for Senate leadership are anonymous. That means relationships will be paramount and the online pro-Trump army won’t know how members voted.

“It’s a loud online presence that doesn’t ultimately add up to votes in the Senate,” said a Senate Republican aide, who requested anonymity to speak candidly about the race’s dynamics. “And senators are reacting negatively to this.”

Most notably, Trump himself hasn’t weighed in as all three candidates seek to show their pro-Trump bona fides.

Scott called Trump in May to ask him for his support in the leadership race, which he said he would appreciate, and his goal is to pressure Trump to announce his support before Wednesday’s election, according to two people with knowledge of his thinking.

In interviews since Election Day, Scott said he and Trump have been communicating by text.

But Scott was coy when he was asked Monday whether he thinks he has Trump’s support.

“I welcome anyone’s support. He supported me in 2022 in my run against Mitch McConnell,” Scott said.

Asked whether he is seeking Trump’s endorsement, he responded, “I am not going to talk about private conversations.”

Lara Trump, a co-chair of the Republican National Committee and Trump’s daughter-in-law, noted Scott has been "very loyal" to Trump in an interview with pro-Trump pundit Benny Johnson on Monday. She stopped short of endorsing him but suggested that voters who like Scott and think he should run the GOP conference should contact their senators.

'Thune's race to lose'

Scott is less popular among his colleagues than Thune and Cornyn; in 2022 he got just 10 votes when he unsuccessfully challenged McConnell for the top job. Thune and Cornyn have well-established relationships as leaders in the conference.

Cornyn's office touted a total of $415 million raised for GOP senators and candidates over his 22 years in the Senate, aided by two terms as the National Republican Senatorial Committee chair.

This cycle, Cornyn's office said, he raised about $33 million for GOP candidates. A source close to Thune touted a similar dollar figure for the 2024 election.

“It’s Thune’s race to lose,” said Mike Davis, a pugnacious Trump ally who previously was a top aide to Senate Republicans.

But Davis said the price of admission for the job will be to advance Trump’s agenda.

“The Senate Republicans — particularly Senate Republican leadership — must understand that the American people put President Trump back in the White House with his America First agenda. And any Republican leader candidate who does not agree with that should get the hell out of the way," he said.

Scott, who just won a second six-year term, said in an interview that his victory in Florida shows that Republicans don’t need to moderate their views.

“We never moderated our positions, and we continued to win,” he said Friday. “Now if you look at the country, we are the center of the Republican Party. … The whole country is headed in our direction.”

Even before last week's elections, Scott had sought to become a bridge between House Speaker Mike Johnson, R-La., and his Senate GOP conference and push McConnell out of relevancy. And with Republicans on track to hold on to a narrow House majority, Scott sees his bond with Johnson as an edge in the leadership race.

A handful of sitting Republican senators have publicly backed him: Ron Johnson of Wisconsin, Marco Rubio of Florida, Rand Paul of Kentucky, Bill Hagerty of Tennessee and Tommy Tuberville of Alabama. The names of some of them, like Rubio, Hagerty and Tuberville, have been floated for senior positions in the Trump administration.

And of the three senators in the running to succeed McConnell, Scott was the only one who did an interview on the Sunday shows this weekend, when he promoted his “close relationship” with the speaker on Fox News.

The interview and the MAGA online campaign were intentional moves to project a flood of support for Scott and put pressure on Thune, who is considered the front-runner.

Trump has made one public demand: The next GOP leader should support his ability to make “recess appointments” to temporarily install personnel without Senate confirmation.

“I’ve spent eight months carefully listening to my colleagues about their vision for the next chapter of the Senate Republican Conference, especially as we hit the ground running with President Trump,” Thune said in a statement. “One thing is clear: We must act quickly and decisively to get the president’s cabinet and other nominees in place as soon as possible to start delivering on the mandate we’ve been sent to execute, and all options are on the table to make that happen, including recess appointments. We cannot let Chuck Schumer and Senate Democrats block the will of the American people.”

Cornyn vowed that if Democrats block Trump’s nominees, “we will stay in session, including weekends, until they relent. Additionally, the Constitution expressly confers the power on the President to make recess appointments.”