ERIE, Pa. — Former President Donald Trump said at a rally here Sunday that Vice President Kamala Harris should be "impeached and prosecuted" for her actions related to the southern U.S. border.

He argued that people were "murdered because of her action at the border, and thousands more will follow in rapid succession," adding, "She should be impeached and prosecuted for her actions."

Trump also lobbed personal attacks at Harris on Sunday, echoing comments at his rally the day Saturday, when he called Harris “mentally disabled” and “mentally impaired.”

With Harris at the top of the Democratic ticket and a tight race in the final stretch of the presidential campaign, Trump's rhetoric has escalated.

Trump has frequently gone after Harris in personal terms, often based on her race and gender.

He has increasingly threatened to go after other political foes if he is elected. He has talked about jailing Facebook co-founder Mark Zuckerberg and discussed possibly carrying out election fraud prosecutions against election officials, donors and operatives.

When she has discussed the border, Harris has often pointed to Trump's role in quashing a bipartisan border deal in Congress in February, which Democrats and several Republicans have said would have addressed aspects of the issue that he frequently invokes on the campaign trail.

"Even though Donald Trump tried to sabotage the border security bill, it is my pledge to you that as president of the United States, I will bring it back up and proudly sign it into law,” Harris said last week during her visit to the U.S.-Mexico border.

An NBC News poll conducted this month found that 54% of registered voters thought Trump would better handle securing the border and controlling immigration, compared with 33% who said the same of Harris. Trump has worked to capitalize on those figures, frequently trying to blame Harris for millions of illegal border crossings since President Joe Biden took office and terming her the administration’s “border czar.”

Trump's comments about Harris' mental fitness echoed attacks he made Saturday at another rally in Wisconsin.

"Joe Biden became mentally impaired. Kamala was born that way," he falsely claimed.

"Think about it: Only a mentally disabled person could have allowed this to happen to our country," he added. "Anybody would know this."

On Sunday, Trump doubled down, saying: "Crooked Joe Biden became mentally impaired — sad. But lying Kamala Harris, honestly, I believe she was born that way."

Minutes later, he called Harris a “stupid person,” and the crowd responded with chants of "lock her up."

Asked for clarification about Trump's comments about Harris' mental state, Trump campaign spokesperson Steven Cheung said Harris is "wholly unfit to serve as president, as evidenced by the shocking ICE numbers that were released last week detailing her abhorrent dereliction of duty of not securing the border allowing murderers, rapists, and convicted criminals to pour into our country to terrorize communities.”

Data from Immigration and Customs Enforcement said 13,000 migrants convicted of homicide are living in the U.S. outside of immigration detention. A spokesperson for the Department of Homeland Security told NBC News that the data goes back four decades, predating the Biden administration.

The Harris campaign did not immediately respond to a request for comment on Trump's remarks on Sunday.

In a statement about Trump's rally Saturday, Harris campaign spokesperson Sarafina Chitika said Trump has "nothing ‘inspiring’ to offer the American people, just darkness."

"The American people deserve better than Trump’s bleak, backward-looking Project 2025 agenda," she added.

Some Republicans also pushed back against Trump's comments on Saturday.

Asked by ABC News whether he approved of Trump's language invoking "mentally impaired" and "mentally disabled," House Majority Whip Tom Emmer, R-Minn., said, "I think we should stick on the issues."

Sen. Lindsey Graham, R-S.C., was confronted with a clip of Trump's remarks during an interview on CNN.

"I just think the better course to take is to prosecute the case that her policies are destroying the country, they're crazy liberal," he said.

Former Maryland Gov. Larry Hogan, a Republican who is running for the Senate, said in a CBS News interview that Trump’s comments were “insulting, not only to the vice president, but to people that actually do have mental disabilities.”

Hogan, whose prospects of winning in blue Maryland would most likely be weakened if he were associated with Trump, has said neither Trump nor Harris has "earned my vote."

Jake Traylor reported from Erie and Megan Lebowitz from Washington.