Donald Trump, the former US president and presumptive presidential nominee of the Republican Party, has attacked Vice President Kamala Harris, raising questions on her competence and describing her as an "insurance policy" for incumbent President Joe Biden.

His attack against Harris, who is of Indian and African heritage, came amid chatter in the Democratic Party about whether President Biden should remain the nominee in the November 5 presidential election.

Biden, 81, has faced calls from some Democrats to step aside as the nominee following his disastrous performance during a June 27 debate with Trump in which he struggled to complete sentences or land any significant blows against his opponent.

“Whatever else can be said about crooked Joe Biden, you have to give him credit for one brilliant decision, probably the smartest decision he ever made. He picked Kamala Harris as his vice president. No, it was brilliant. Because it was an insurance policy. Maybe the best insurance policy I’ve ever seen,” Trump, 78, told his supporters in Florida.

“If Joe had picked someone even halfway competent, they would have bounced him from office years ago, but they can’t because she’s gotta be their second choice,” he said as he repeatedly mispronounced her name.

Trump said as vice president, Harris was given two very important tasks - border security and to deter Russia from attacking Ukraine.

"First, she was put in charge of the U.S. border security. She never showed up. She's never gone. She never went there once. And the border is the worst border in the history of the world,” he alleged.

“We have the best border in history because she has the worst border in the history of the world. Then, she was sent to Europe to deter Russia from attacking Ukraine. How did that work out? Not too good. Both times, the result was a deadly failure. Since Kamala was made border czar, the Biden-Harris administration has lost track of an estimated 150,000 children, many of whom have undoubtedly been raped, trafficked, killed, or horribly abused,” Trump said.

Trump accused Harris, 59, of being a socialist.

“I don't think Kamala Harris' California socialism is going to go down well with the people of Doral, the people of Miami, or the people of Florida. Because in Florida, we don't like socialism. We want our freedom, right? We want our freedom,” he said.

“Joe, Kamala and the entire Democrat establishment have been caught red-handed in the thick of the biggest scandal and the biggest coverup…it’s a cover-up. It’s the biggest cover-up in political history. As you know, they are all co-conspirators in the sinister plot to defraud the American public about the cognitive abilities of the man in the Oval Office,” alleged Trump.

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