[WASHINGTON – President Donald Trump on Tuesday attacked Sen. Kamala Harris over her questioning of Supreme Court Justice Brett Kavanaugh during his confirmation hearings in his first public remarks since she was named Joe Biden's running mate.

Harris, a former prosecutor, grilled the judge over sexual misconduct allegations against him during the contentious 2018 confirmation hearings.

"And the horrible way she treated Justice Kavanaugh, that was a horrible event. I thought it was terrible for her, I thought it was terrible for our nation," Trump told reporters during a White House briefing. "I thought she was the meanest, the most horrible most disrespectful of anybody in the U.S. Senate."

Trump saved his remarks on Harris for the scheduled briefing. But minutes after the announcement, Trump tweeted a new campaign attack ad on Harris, a vocal critic of the president. The ad accuses Biden of "handing over the reins to Kamala while they jointly embrace the radical left."

"She is also known, from what I understand, as being just about the most liberal person in the U.S. Senate and I would have thought Biden would have tried to stay away from that a little bit," Trump said.

Biden announced Harris, one of his former Democratic primary challengers, as his No. 2 pick after weeks of speculation in the lead-up to next week's Democratic convention. She will become the first Black woman and first Asian American person on a major party's presidential ticket.

Following the announcement, the Trump campaign seized on a feisty exchange between Harris and Biden during a June 2019 Democratic debate, when the California senator was still in the race. Harris challenged Biden over his remarks about working with segregationist senators and criticized him for his previous opposition to federal busing mandates – a moment that hobbled his campaign and led to her brief surge in national polls.

"Not long ago, Kamala Harris called Joe Biden a racist and asked for an apology she never received. Clearly, Phony Kamala will abandon her own morals, as well as try to bury her record as a prosecutor, in order to appease the anti-police extremists controlling the Democrat Party," Trump senior adviser Katrina Pierson said in a statement Tuesday.

"She is proof that Joe Biden is an empty shell being filled with the extreme agenda of the radicals on the left," Pierson added.