Prairie du Chien, Wisconsin - Republican candidate Donald Trump had some harsh things to say about his Democratic rival Kamala Harris after her recent visit to the country's southern border.

On Saturday night, Trump held a rally at the Prairie Du Chien Area Arts Center, where he delivered a fiery speech, surrounded by large posters with the faces of undocumented immigrants who have been accused of violent crimes.

He criticized Harris for her recent trip to Douglas, Arizona, blaming her administration's policies for the crimes and describing her speech at the border as "bulls**t."

"She is a disaster, and she is not ever going to do anything for the border," Trump lamented.

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The former president went on to take his regular criticisms of Harris' intelligence to a whole new level.

"Joe Biden became mentally impaired; Kamala was born that way," Trump told his MAGA crowd, garnering roaring cheers of agreement.

"And if you think about it, only a mentally disabled person could have allowed this to happen to our country," he added.

Trump, who appeared angrier than usual, acknowledged that his rhetoric that evening was darker than some may have expected.

"Isn't this a wonderful and inspiring speech?" he said sarcastically, later adding, "I'm just saying – this is a dark speech."

Trump's latest comments come as he and his running mate, JD Vance, make immigration a central focus of their campaign, promising to enact the largest deportation effort in US history on day one if they win.

They have consistently blamed Biden and Harris' immigration policies for specific incidents of crime involving undocumented immigrants and regularly refer to Harris as the "border czar," despite the fact that she was never appointed to such a position.

During his rally, Trump also described immigrants who commit crimes as "stone-cold killers" who will "walk into your kitchen, [and] cut your throat."

In a statement, the Harris campaign said Trump's "dark" speech "did not offer a single policy" that would help voters, adding he is more interested in "fanning the flames of hate and division."