Democratic presidential candidate Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE condemned President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE's remarks Tuesday about a White House official who is testifying in the impeachment inquiry.

Biden, in an interview with MSNBC, called the president's negative tweet about Lt. Col. Alexander Vindman "despicable." He went on to laud the National Security Council's European affairs director, calling him a "hell of a patriot."

"This guy won the Purple Heart, this guy's a hero, this guy's a patriot," said the former vice president. "It's despicable to do this. ... This guy is a patriot."

"I've never met him, but he's a hell of a patriot," he added of Vindman.

Biden calls Trump despicable and says Vindman is a hell of a patriot. #Vindman pic.twitter.com/3wSSuBd7FS — PoliticusUSA (@politicususa) October 29, 2019

Biden's comments follow a Tuesday tweet in which Trump criticized Vindman, who was slated to testify Tuesday.

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“Supposedly, according to the Corrupt Media, the Ukraine call ‘concerned’ today’s Never Trumper witness. Was he on the same call that I was?" Trump wrote. "Can’t be possible! Please ask him to read the Transcript of the call. Witch Hunt!”

House Democrats launched an impeachment inquiry into President Trump last month after a whistleblower complaint filed to Congress revealed that Trump asked the president of the Ukraine to investigate Biden and his son Hunter Biden.

Vindman is expected to tell lawmakers Tuesday that he twice reported concerns about Trump's dealings with Ukraine, according to a copy of his opening statement obtained by The Hill.

“I did not think it was proper to demand that a foreign government investigate a U.S. citizen, and I was worried about the implications for the U.S. government’s support of Ukraine,” the statement said. “I realized that if Ukraine pursued an investigation into the Bidens and Burisma it would likely be interpreted as a partisan play which would undoubtedly result in Ukraine losing the bipartisan support it has thus far maintained.”

Biden is among more than a dozen people running for the 2020 Democratic presidential nomination.