WASHINGTON (Reuters) - U.S. President Donald Trump on Tuesday called the public congressional impeachment hearings “a disgrace” and an “embarrassment” to the nation, but said it was up to Americans to make their own judgment about the witness testimony.

Trump, who has previously tweeted attacks on several U.S. civil servants testifying in the probe, said he did not know one of the key witnesses testifying on Tuesday whom he had previously called a “Never Trumper.”

Army Lieutenant Colonel Alexander Vindman, the White House National Security Council’s top Ukraine expert, and Jennifer Williams, an aide to U.S. Vice President Mike Pence, were among four witnesses testifying before lawmakers on Tuesday in the ongoing impeachment inquiry led by House Democrats.

“What’s going on is a disgrace, and it’s an embarrassment to our nation,” Trump told reporters at the White House at a meeting of his Cabinet. “It’s a big scam”

“I never saw the man, I understand now he wears his uniform when he goes in. No, I don’t know Vindman at all,” Trump said, adding that he had watched part of his testimony.

“I’m going to let people make their own determination,” Trump said, adding: “I never heard of any of these people other than I have seen one or two a couple of times -- they’re ambassadors.”