“That guy’s a Purple Heart. I think it would be a mistake to attack his credibility,” South Dakota Sen. John Thune, the No. 2 Senate Republican, said in an interview. “You can obviously take issue with the substance and there are different interpretations about all that stuff. But I wouldn’t go after him personally. He’s a patriot.”

“I’m not going to question the patriotism of any of the people who come forward," said Senate Majority Leader Mitch McConnell (R-Ky.), though he declined to comment "on the merit of what’s going forward" or Vindman's suggestion that he was concerned Trump's actions had undermined national security.

Rep. Liz Cheney of Wyoming, one of the most hawkish Republicans in the House and a member of the Armed Services Committee, said it would be “shameful” to question Vindman’s loyalty or patriotism to the country.

Cheney wasn’t even pressed by reporters on the topic; in her opening remarks during a weekly leadership news conference in the Capitol, she went out of her way to decry the attacks on Vindman, including the outlandish theory that he was a potential spy working against the United States.

“We need to show that we are better than that as a nation,” said Cheney, the third-ranking House Republican. “We’re talking about decorated veterans who have served this nation, who put their lives on the line. And it is shameful to question their patriotism, their love of this nation, and we should not be involved in this process.”

"This is the career military officer with a Purple Heart? I'm sure he's doing his best to serve his country," said Sen. Roy Blunt of Missouri, the No. 4 GOP leader. "Somebody can have a wrong sense of where they think the path goes but that doesn't mean that they're wrongly motivated. ... Criticizing this guy? No. I wouldn't be on board."

Former Rep. Sean Duffy (R-Wis.) said on CNN that Vindman seems “incredibly concerned about Ukrainian defense. I don’t know that he’s concerned about American policy,” adding that Vindman’s “affinity” may be for Ukraine not the United States.

Trump also attacked Vindman as a "Never Trumper witness" on Tuesday.

But it appeared the criticism from Duffy's former colleagues was having an effect. Duffy tweeted later Tuesday that Vindman is an "American war hero," and that the point he was trying to make is that "Mr. Vindman is an unelected advisor, he gives ADVICE. President Trump sets the policy."