Donald Trump spoke on Saturday in the battleground state of Wisconsin, escalating his anti-immigrant rhetoric and taking his personal insults against Kamala Harris up a notch.

Trump’s speech in the small community of Prairie du Chien, where a Venezuelan in the US illegally was detained in September for allegedly sexually assaulting a woman and attacking her daughter, was unusually devoted almost entirely to undocumented immigrants. He wrongfully claimed that immigrants in the US are violent criminals, referring to them as “stone-cold killers”, “monsters” and “vile animals”.

The Republican presidential candidate was flanked by posters of immigrants in the US illegally who have been arrested for murder and other violent crimes, and banners saying “End Migrant Crime” and “Deport Illegals Now”.

Trump is locked in a close race with Kamala Harris, the Democratic candidate and vice-president, before the 5 November election. Immigration at the southern border are one of the top issues for voters, according to opinion polls.

Trump attacked Harris, who on Friday visited the US-Mexico border for the first time in her 2024 presidential campaign, calling her “mentally impaired” and “mentally disabled”.

The former president blamed Harris and Joe Biden for allowing undocumented immigrants into the US, accusing some immigrants of wanting to “rape, pillage, thieve, plunder and kill the people of the United States of America”.

At one point Trump admitted: “This is a dark speech.”

“There’s no greater act of disloyalty than to extinguish the sovereignty of your own nation right through your border, no matter what lies she tells,” he said.

“Kamala Harris can never be forgiven for her erasing our border, and she must never be allowed to become president of the United States and Wisconsin,” he added.

A video intending to attack Kamala Harris was shown in the middle of Trump’s remarks.

It was a compilation of Harris’s comments about immigration policy.

“She is a disaster, and she’s not going to ever do anything for the border,” he said after the video. “She’s incompetent and a bad person.”

“She’s a Marxist,” he added.

JD Vance continued the attacks on Harris in a speech in Newton, Pennsylvania, taking the former president’s lead and making sure to continue the anti-immigrant claims.

“The problem with Kamala Harris is that she’s got no substance,” Trump’s running mate said. “The problem with Kamala Harris is that she’s got no plan. And the problem with Kamala Harris is that she has been the vice-president for three-and-a-half years and has failed this country.”

Vance claimed without proof that Harris played a role in worsening the economy by exacerbating inflation, then went on to link the country’s economic woes to immigration, blaming Harris for what he describes as an “invasion” amid a lack of border control.

Vance claimed that the presence of immigrants in the US is contributing to rising housing costs.

Some 7 million immigrants have been arrested crossing the US-Mexico border illegally during Biden’s administration, according to government data, a record high number that has fueled criticism of Harris and Biden from Trump and fellow Republicans.

In her visit to the border on Friday, Harris outlined her plans to fix “our broken immigration system” while accusing Trump of “fanning the flames of fear and division” over the impact of immigrants on American life.

Harris also called for tighter asylum restrictions and vowed to make a “top priority” of stopping fentanyl from entering the US.

Before wrapping up his speech, Trump called to the stage the mother of Rachel Morin, a 37-year-old Maryland mother of five who was killed last year. After Rachel’s death, a native of El Salvador was arrested. Trump has used this case to support his remarks against immigrants from Central America living in the US.

Studies generally find there is no evidence immigrants commit crimes at a higher rate than native-born Americans and critics say Trump’s rhetoric reinforces racist tropes.

Trump’s opponents accuse him of cynically exploiting grieving families to fuel his narrative that foreign-born, often Hispanic, arrivals are part of an invading army.

But some of the families of the victims have welcomed Trump’s focus on the issue of violent crime and the death toll of teenagers caused by the opioid drug fentanyl, much of which crosses into the US over the southern border.