Heading into the final stretch of the 2024 campaign, Donald Trump is using increasingly shocking and harsh rhetoric to go after Vice President Kamala Harris and to paint a picture of a country being "destroyed."

He's now calling Harris "mentally impaired" and even "disabled." Illegal immigrants, he claimed over the weekend, will come into American homes and slit people's throats. A single day of "violent" policing, he argued, would address the issue of crime in the U.S.

At one point while speaking to rallygoers in battleground Pennsylvania on Sunday, Trump himself acknowledged, "This is a dark speech."

The language comes as polls show a tight race with just 36 days until Election Day as of Monday. National averages compiled by 538 show Harris up by less than 3 percentage points. In key swing states, the margin is even closer.

"He's clearly feeling the heat, so he's reverting to what he knows best and what he believes has always helped him in the past," said Daniel Schnur, a professor at the University of California Berkeley and former political strategist.

Trump is no stranger to inflammatory rhetoric. A hallmark of his 2016 bid for the White House was to cast immigrants as rapists and drug traffickers.

Though at a campaign stop in Wisconsin on Saturday, Trump went much further -- despite the fact that U.S. citizens commit crimes at higher rates than undocumented immigrants.

"And you remember when they say no, no, these are migrants and these migrants, they don't commit crimes like us," Trump said. "No, no, they make our ​​criminals look like babies. These are stone cold killers. They'll walk into your kitchen, they'll cut your throat."

He also employed his harshest attack on Harris yet this cycle, baselessly calling her "mentally impaired" as he went after the Biden-Harris administration's handling of the southern border.

"Joe Biden became mentally impaired," he said. "Kamala was born that way. She was born that way. And if you think about it, only a mentally disabled person could have allowed this to happen to our country."

Jennifer Mercieca, a historian of political rhetoric at Texas A&M University, said while Trump has a history of divisive rhetoric, the "very graphic depiction of the consequences of not voting for him is new."

"He's intensifying his language," Mercieca said. "I think that could be a strategy just to get more attention. But at the same time, the things that he's saying are not true."

Mercieca called such fear appeals by Trump "incredibly irresponsible" given the current heated political environment.

Mark Weaver, a Republican strategist, defended Trump's rhetoric as a blunt way to highlight Harris' sometimes meandering answers and some gruesome crimes committed by immigrants in the U.S. illegally.

"Voters know that he talks the way they do, which is to say not scripted by political handlers," Weaver said.

Schnur said Trump's comments about Harris and about migrants are "designed to motivate his base, but it's a bigger question whether it does him any good with swing voters."

But longtime GOP strategist Charlie Black questioned any advantage to Trump's comments.

"All of Trump's campaign staff and advisers, as well as all of his friends and surrogates in Congress, think this kind of rhetoric is wrong and is hurting his campaign," Black said. "They are right."

Republican lawmakers and pundits were peppered with questions about Trump's comments as they made the rounds on Sunday talk shows.

House Majority Whip Tom Emmer, R-Minn., sidestepped directly criticizing Trump's comments but said on ABC's "This Week" that he believed the former president should "stick to the issues."

Sen. Lindsey Graham, R-S.C., had a similar view as he appeared on CNN's "State of the Union" -- though he did say he did not think Harris had a mental disability.

"I just think the better course to take is to prosecute the case that her policies are destroying the country," Graham said.

The Harris campaign has often highlighted Trump's more controversial remarks by sharing clips of his rallies online. They did so with some of his eyebrow-raising remarks over the weekend, including his musing that one "violent" or "real rough" day of police crackdown would deter retail theft. A Trump campaign official later told Politico the comment was "made in jest."

While Harris nor her campaign have directly responded to his attacks on her mental state, spokeswoman Sarafina Chitika put out a statement over the weekend saying the "American people deserve better than Trump's bleak, backward-looking Project 2025 agenda."

"Donald Trump is finally telling the truth to voters: He's got nothing 'inspiring' to offer the American people, just darkness," Chitika said.

ABC News has reached out to Trump's campaign for comment.