Donald Trump is repurposing an old attack line against a new opponent, labeling vice president Kamala Harris "mentally impaired."

Speaking at a rally in Erie, Pennsylvania on Sunday, Trump speculated that Harris has "something wrong" with her after she and Joe Biden allowed millions of illegal immigrants to pour across the southern border.

Trump's new insult

Indeed, the border crisis has become such a liability for Democrats that Harris went to Arizona on Friday for a photo-op, drawing criticism from Republicans who say she is whitewashing the Biden-Harris administration's record.

A day later, Trump told a crowd in Wisconsin that "only a mentally disabled person" would allow the massive influx of illegal immigrants that Biden and Harris have overseen.

At another rally in Pennsylvania on Sunday, Trump continued with the theme that Harris is mentally unfit for duty.

"There’s something wrong with Kamala, and I just don’t know what it is, but there is definitely something missing. And you know what? Everybody knows it,” he said.

In addition to calling Harris unqualified, Trump has said Harris should be impeached and prosecuted for mishandling the border.

Just like Biden?

Harris does not have any known health problems, but her frequent verbal gaffes have led some to compare her to her boss Joe Biden, long rumored to be in cognitive decline.

Trump has continued to mock Harris as unintelligent, over the objections of Republicans in Washington who argue his rhetoric is a distraction from policy issues.

“Crooked Joe Biden became mentally impaired — sad. But lyin’ Kamala Harris, honestly, I believe she was born that way," Trump said in Erie on Sunday.

Harris hasn't shied from using personal attacks against Trump, belittling his crowd sizes and accusing him of the worst attack on American democracy since the Civil War - but she hasn't faced the same kind of pressure as Trump to lower her tone.

Trump doubles down

Democrats anointed Harris their presidential nominee in an unprecedented, 11th-hour move after doubts about Biden's mental fitness exploded into public view, following his debate with Trump in June.

Harris outperformed expectations at her first and potentially only debate with Trump on September 10, where she appeared to rattle Trump by mocking his crowd sizes. The Harris campaign has been pushing for a second debate, but Trump has refused, saying it's too late with early voting underway.

The Harris campaign is eager for a second debate because of her difficulties with television interviews, where she often has trouble speaking extemporaneously.

After Harris shared an image that purported to show her responding to Hurricane Helene, Trump noticed that her headphones appeared to be unplugged.

"You have to plug the cord into the phone for it to work!" Trump wrote in the post Monday. "Another fake and staged photo from someone who has no clue what she is doing."