Mr Trump and Mr Biden are ramping up their campaigns for President as the November 3 election draws nearer. Mr Biden announced Mrs Harris as his running mate after she originally ran against him, with the two sparring at Democrat primary debates. Mrs Harris previously was the Attorney General of California, and is now the senator for the state.
Mr Trump’s campaign posted adverts on social media showing Mrs Harris blasting her now-running mate in the primaries.
She previously accused Mr Biden of “working with segregationists”, and spotlighted his opposition to school busing for young African-Americans.
In the attack ad, Mr Trump’s campaign branded Mrs Harris a “phony” after “attacking Joe Biden for racist policies”.
The video also labelled Mrs Harris as part of the “radical left”.
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Mr Trump also hit out at Mrs Harris in a press conference at the White House, and questioned why Mr Biden made her his “number one pick”.
He added: “I was a little surprised that he picked her.”
Mr Trump pointed to Mrs Harris’ Democrat primaries performance and said “she did very, very poorly”.
He also branded Mrs Harris as “nasty” and “disrespectful” to the former Vice President Mr Biden.
Mrs Harris dropped out of the Democrat primaries in December, and threw her support behind Mr Biden despite the pairs conflict on stage.
Mr Biden tweeted that he had “the great honour” to name Ms Harris as his running mate, and described her as “a fearless fighter for the little guy, and one of the country’s finest public servants”.
He added that she had worked closely with his late son, Beau, when she was California’s attorney general.
He said: “I watched as they took on the big banks, lifted up working people, and protected women and kids from abuse.
“I was proud then, and I’m proud now to have her as my partner in this campaign.”
Mr Trump’s attacks on Mrs Harris came as it was revealed that the US president had donated to the new Democrat running mate twice.
He donated $5,000 to Mrs Harris in 2011, and $1,000 in 2013, according to California public records for state donations.
Both donations came as Mrs Harris was running as an Attorney General candidate, and while Mr Trump was a private citizen.
A spokeswoman for Mrs Harris confirmed to the Sacramento Bee that she received Mr Trump’s donations, but they were given to a non-profit group to assist Central Americans in 2015.