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 said Tuesday that he does not know Lt. Col. Alexander Vindman Alexander VindmanImpeachment witness Alexander Vindman calls Trump Putin's 'useful idiot' The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Strzok: Trump behaving like an authoritarian MORE, the White House national security official testifying in connection with the House impeachment inquiry, and said he would let others make up their minds as to his credibility.

“I never saw the man. I understand now he wears his uniform when he goes in,” Trump told reporters at the White House during a Cabinet meeting on Tuesday when asked if Vindman was credible, tacitly questioning Vindman's decision to dress in his military uniform. “No, I don’t know Vindman at all. What I do know is that he said the transcript was correct.”

“Vindman, I watched him for a little while this morning, and I think he — I’m going to let people make their own determination,” Trump, who last month called Vindman a “Never Trumper,” continued.

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His remarks came as Vindman testified on Capitol Hill about a July 25 phone call he listened in on between Trump and Ukrainian President Volodymyr Zelensky.

“I don’t know, as he says, Lieutenant Colonel. I understand somebody had the misfortune of calling him 'mister' and he corrected them,” Trump said, referencing a moment during Tuesday’s hearing during which Vindman corrected Rep. Devin Nunes Devin Gerald NunesOvernight Defense: Stopgap spending measure awaits Senate vote | Trump nominates former Nunes aide for intelligence community watchdog | Trump extends ban on racial discrimination training to contractors, military Trump nominates former Nunes aide to serve as intel community inspector general Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election MORE (R-Calif.), one of the president’s Capitol Hill allies, when he misstated his title.

Trump's comment about Vindman's uniform came after Rep. Chris Stewart Christopher (Chris) Douglas StewartAtlanta Wendy's 911 call the night of Rayshard Brooks's death released Tyler Perry offers to pay for funeral of Rayshard Brooks Current, former NHL players form diversity coalition to fight intolerance in hockey MORE (R-Utah) asserted at the hearing that Vindman was wearing his uniform on Capitol Hill despite normally wearing a suit to work — amplifying reports in conservative media suggesting he was doing so for show.

“I’m in uniform wearing my military rank. I thought it was appropriate to stick with that. The attacks that I’ve had in the press and Twitter have marginalized me as a military officer,” Vindman responded to Stewart.

Trump on Tuesday also sought to distance himself from other witnesses, including State Department officials William Taylor and George Kent, both of whom testified last week.

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“I don’t know any of these people, other than I have seen one or two a couple of times,” Trump told reporters. “I don’t know who Kent is. I don’t know who Taylor is.”

The July 25 call — during which Trump asked Ukraine for investigations into 2016 election interference as well as former Vice President 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 and his son Hunter Biden’s business dealings with a Ukrainian gas company — is at the heart of House Democrats’ impeachment inquiry into Trump.

The president has insisted that the call, a rough transcript of which has been released by the White House, was “perfect” and that he did nothing wrong.

“What is going on is a disgrace and it’s an embarrassment to our nation,” Trump told reporters Tuesday, calling House Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) “grossly incompetent” and accusing her of focusing on impeachment instead of passing the new United States-Mexico-Canada Trade Agreement (USMCA).

Witnesses like Taylor, however, have described an effort by Trump administration officials to use a White House meeting and aid to Ukraine to press Kyiv for investigations sought by the president.

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Vindman, who told lawmakers on Tuesday that he never had any contact directly with Trump, said that the call was “improper” and that he reported it to the National Security Council’s top lawyer out of a “sense of duty.”

“I was concerned by the call. What I heard was improper, and I reported my concerns to Mr. [John] Eisenberg,” Vindman said Tuesday. “It is improper for the president of the United States to demand a foreign government investigate a U.S. citizen and political opponent.”

“It was also clear that if Ukraine pursued an investigation into the 2016 election, the Bidens and Burisma, it would be interpreted as a partisan play. This would undoubtedly result in Ukraine losing bipartisan support, undermine U.S. national security and advance Russia’s strategic objectives in the region,” Vindman continued.

Vindman, who also testified privately in connection with the inquiry last week, is one of several officials slated to testify this week about the Trump administration’s dealings with Ukraine.

Trump has questioned the credibility of witnesses as well as the whistleblower who filed a complaint about the call that alleged Trump used his office to solicit foreign interference in the 2020 election.

Trump criticized Vindman as a “Never Trumper” in a tweet last month before his closed-door testimony and has launched similar criticisms against Taylor. Trump has at times sought to distance himself from other witnesses like U.S. Ambassador to the European Union Gordon Sondland Gordon SondlandGOP chairman vows to protect whistleblowers following Vindman retirement over 'bullying' Top Democrat slams Trump's new EU envoy: Not 'a political donor's part-time job' Trump names new EU envoy, filling post left vacant by impeachment witness Sondland MORE.

Trump’s remarks Tuesday on Vindman were muted when compared to his statements about ousted U.S. Ambassador to Ukraine Marie Yovanovitch Marie YovanovitchGrand jury adds additional counts against Giuliani associates Lev Parnas and and Igor Fruman Strzok: Trump behaving like an authoritarian Powell backs Biden at convention as Democrats rip Trump on security MORE, who at a public hearing on Friday recounted a smear campaign she faced from Trump’s personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE.

Trump lashed out at Yovanovitch on Twitter, claiming that “everywhere” she went as a foreign service officer “went bad.” Democrats quickly accused the president of witness intimidation.

--This report was updated at 2:48 p.m.