Former US President Donald Trump launched a volley of attacks against US Vice President Kamala Harris Wednesday, calling her a "radical left lunatic" in his first rally since she became the de facto Democratic Party nominee for November's election.

In a speech where he also claimed that Harris was in favor of the "execution" of babies due to her position on abortions, the former president and Republican nominee said: "She is a radical left lunatic who will destroy our country," AFP reports.

Trump's address comes as Kamala Harris, 59, hits the campaign trail armed with President Joe Biden's endorsement -- after his historic decision over the weekend not to seek reelection.

Donald Trump had been attacking Biden over his age, but is now being forced to pivot as he has become the oldest nominee in US history.

Trump turned his aim at Kamala Harris on Wednesday, saying she was "the ultra liberal driving force behind every single Biden catastrophe."

From dubbing her "Lyin' Kamala" to alleging that her record on the border has allowed communities to be "ravaged by migrant crime," he charged that "she's unfit to lead."

He also raised the politically explosive issue of abortion, after Harris pledged to put abortion rights at the center of her campaign and to fight for the right to control one's own body.

"She wants abortions in the eighth and ninth month of pregnancy. That's fine with her, right up until birth and even after birth, the execution of a baby," Trump claimed.

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