WASHINGTON (Reuters) - Donald Trump's campaign billed the event at a Michigan manufacturing plant as an address by the Republican presidential candidate on the local economy. Residents of the battleground state, aides noted in advance, were being hit hard by inflation.

But with rolls of insulated building materials as a backdrop and workers in the audience, Trump spent the first 25 minutes of the speech on Sept. 27 railing about border security and migrants streaming into the country. His words grew increasingly graphic as he did so.

Migrants who had come across the U.S. border were slaughtering people across the country, he falsely claimed.

"These are people at the highest level of killing that cut your throat and won't even think about it the next morning," Trump told the crowd. "They grab young girls and slice them up right in front of their parents."

The Trump campaign did not respond to questions on what evidence Trump had to support those statements.

In the final weeks of the election campaign, Trump is increasingly resorting to darker and more violent language about illegal immigration at the southern U.S. border with Mexico, an issue that opinion polls show resonates with many voters, especially Republicans.

Trump has for years portrayed migrants as invaders and criminals, and during his 2017-2021 presidency took stringent steps to curb legal and illegal migration from around the world. He is promising the biggest deportation effort in U.S. history if he is elected on Nov. 5.

As Election Day nears and opinion polls show an ever tightening race with his Democratic rival, Vice President Kamala Harris, Trump's language about migrants has become more apocalyptic and graphic in what his critics say is an effort to amplify racist tropes and exploit Republican voter fears about millions of border crossers entering the U.S.

That comes despite the White House instituting new restrictions that have sharply limited the number of migrants entering the country. Trump earlier this year helped sink a bipartisan bill in Congress that would have fortified security at the border.

`BLIGHTED REFUGEE CAMPS`

As recently as August, Trump was content to describe border-crossers as "killers" or "terrorists," in a more generalized way. Now, he is adding lurid accounts of women allegedly being victimized by migrants, speaking of "savages" and "predators" who "sexually assault" young girls while referring to small towns in America as "blighted refugee camps."

A range of studies show immigrants do not commit crime at a higher rate than native-born Americans.

"President Trump is fighting to ensure that no other family endures the tragedy of losing a child at the hands of an illegal immigrant, and only he will make America safe again," said Anna Kelly, a spokesperson for the campaign.

Immigrant rights advocates say Trump is also increasingly scapegoating immigrants for a host of the nation's ills, from unemployment to access to medical care to overcrowding in schools to housing affordability.

The campaign has not provided evidence for these assertions.

While studies show increased low-skilled immigration can drive down wages among native-born Americans without a high school diploma, immigration is bolstering a U.S. workforce that would otherwise be set to decline as older workers retire.

Trump, who draws much of his support from non-college educated white males, has also spent the past few months laying the groundwork for blaming a loss in the election on non-citizens voting in large numbers - something that is illegal and for which there is little evidence.

"His rhetoric is becoming more cruel, more dehumanizing, with the goal of stirring anger and hate," said Vanessa Cardenas, executive director of America's Voice, an advocacy group that backs immigration reform. "It is painting a whole population as subhuman."

In doing so, Trump also has blurred the distinction between legal and illegal immigration. He has often cast immigrants in the country legally - such as much of the Haitian population of Springfield, Ohio, whom Trump falsely accused last month of eating household pets in what has been a longstanding racial stereotype - as pariahs who must be removed.

`THIS IS A DARK SPEECH'

A hallmark of Trump's turn toward darker language is the more graphic description of violence allegedly meted out by migrants.

At a rally in the small Wisconsin town of Prairie du Chien last weekend, Trump suggested migrants want to "rape, pillage, thieve, plunder and kill" the nation's citizens and that they would "walk into your kitchen, they'll cut your throat."

Even he seemed to be momentarily taken aback by his language. "This is a dark speech," he acknowledged.

In a speech the next day in Erie, Pennsylvania, he cited several instances of rape, including child rape, that he said came at the hands of migrants in the country illegally.

To be sure, there have been cases of assaults and murders in the U.S. in which migrants have been implicated. But rather than offering them as anecdotes, Trump has falsely asserted the episodes are proof that all migrants pose a threat.

Most states and cities do not track the immigration status of alleged criminal offenders or make such data available. Some jurisdictions explicitly prohibit collecting that information.

At rallies, Trump has largely detailed crimes against mostly young, often white, women, which is built upon a historical trope of dangerous men of color.

Daniel Treisman, a professor at the University of California, Los Angeles, who has analyzed Trump's speeches dating back to 2015, said there has been a "long upward trend" toward Trump embracing a more violent vocabulary since he first ran for president in the 2016 election.

Treisman said Trump's speech in Erie was among the harshest that he has tracked.

"That speech was far more violent than his speeches in the fall of 2016 or 2020," Treisman said.

Trump's message connecting migrants to crime seems to be breaking through.

A poll released last month by KFF, a health policy news outlet, showed that 80% of Americans surveyed had heard false statements about the influx of migrants leading to an increase in violent crime and 74% had heard that immigrants were taking jobs away from citizens and contributing to a rise in unemployment.

According to the poll, a majority of independent voters - 53% - said that the claims tying migrants to a spike in crime were "definitely true or probably true."

"It's absolutely penetrating. The impact it has on winning new votes is an open question," said Drew Altman, president and CEO of KFF. "This is Trump's version of a game of inches."