Without evidence, Trump calls White House official 'Never Trumper' ahead of impeachment testimony Army Lt. Col. Alexander Vindman was wounded in an IED attack in Iraq.

President Donald Trump on Tuesday attacked a White House National Security Council official as a "Never Trumper" just before he was to tell House impeachment investigators he raised alarms about what Trump told Ukraine's president during a July phone call.

Army Lt. Col. Alexander Vindman, the National Security Council's Director of European Affairs, arrived on Capitol Hill Tuesday morning ahead of a closed-door deposition as part of the House's impeachment inquiry. Vindman, who listened to the phone call between Trump and Ukrainian President Volodymyr Zelenskiy, became the first current White House official to testify in the probe despite a blanket White House directive against doing so.

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

Trump has repeatedly lambasted these officials sitting for depositions as “Never Trumpers” – he called the United States’ top diplomat in Ukraine, Bill Taylor, one, too – despite the fact that there’s no evidence they have political biases against Trump and despite both officials having long records of service for the United States.

Vindman planned to tell House impeachment investigators that he was "concerned by the call," according to a copy of his opening remarks obtained by ABC News.

"I was concerned by the call. 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," Vindman planned to say.

Vindman immigrated to the United States from Ukraine as a child, has served in the Army and was wounded in an IED attack in Iraq, and received a Purple Heart.

Despite Vindman's career serving in the U.S. military and government, conservative defenders of the president attacked Vindman's loyalty by focusing on his heritage.

"We also know he was born in the Soviet Union, immigrated with his family, young," "Fox and Friends" host Brian Kilmeade said Tuesday morning. "He tends to feel simpatico with the Ukraine."

"It seems very clear that he is incredibly concerned about Ukrainian defense,” former U.S. Rep. Sean Duffy, a Republican from Wisconsin, said on CNN Tuesday morning. “I don't know that he's concerned about American policy, but his main mission was to make sure that the Ukraine got those weapons. I understand that. We all have an affinity to our homeland where we came from."

Responding to a question from a Fox News host Monday night that broached Vindman's Ukrainian background, John Yoo, a former Justice Department official under President George W. Bush, said that "some people might call" Vindman's interactions with Ukrainian officials "espionage."

But not all Republicans agreed with that line of attack.

Sen. Mitt Romney, Republican of Utah, called the attacks “absurd and terribly unfortunate,” and Rep. Liz Cheney, a Republican from Wyoming, said it was “shameful” that some Republicans like Duffy have questioned the patriotism of witnesses like Vindman.

“I think we need to show we are better than that as a nation,” Cheney said. “Their patriotism, their love of country – we’re talking about decorated veterans who have served this nation, who have out 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 that process.”

GOP Sen. Kevin Cramer of North Dakota said “attacks on individuals don't make a lot of sense to me, in general.” He added, “"I think personal attacks just aren't helpful, frankly.”

Democratic senators echoed that defense of Vindman.

"I think it's despicable for anybody, especially an elected official, to criticize an honored military veteran who's served our country valiantly and basically is willing to sacrifice their life for us," Democratic Sen. Joe Manchin, of West Virginia, said. "To drag them through this situation and demean them to the point where they are not supposed to be credible, I just think that's wrong.”

Fellow Democrat Sen. Mazie Hirono, of Hawaii, called the attacks “pathetic” and showed that Republicans “can't defend the president's conduct so basically they are attacking a war hero who continues to serve our country.”

"Republicans got nothing!” Hirono added. “That's why what they're doing is pathetic and if anybody is unpatriotic it's those people who attack a decorated war hero who continues to serve our country.”

Meanwhile, House Minority Leader Kevin McCarthy said that he thanked Vindman for his service, but said he is “wrong” in believing that comments he heard from the president during the July 25 call with the Ukraine president were of national security concern.

“We have a difference of opinion but we also have rule of law,” McCarthy, R-Calif., said, pointing at a summary transcript released by the White House. “Nothing is impeachable,” he said, arguing there is no quid pro quo.

Vindman was not the first official Trump has lambasted as a "Never Trumper" despite citing no evidence showing they harbor any political biases against the president.

On Friday, Trump told reporters at the White House that Taylor was "a Never Trumper and his lawyer is a Never Trumper." He did not provide any evidence to support his claims.

Both Vindman and Taylor are current U.S. officials, the latter called to serve in Ukraine by Secretary of State Mike Pompeo, who was nominated by Trump. Vindman is a current official on the Trump administration's National Security Council.

They have both served under both Democratic and Republican administrations.

Trump on Friday blamed Pompeo for hiring Taylor. "Hey, everybody makes mistakes," the president said. "Mike Pompeo. Everybody makes mistakes. He's a Never Trumper. His lawyer's the head of the Never Trumpers. They're a dying breed but they're still there."

Trump has also invoked espionage to refer to those who have raised questions about his dealings with Ukraine.

“I want to know who’s the person who gave the whistleblower the information because that’s close to a spy,” Trump said at the U.S. Mission to the United Nations last month. “You know what we used to do in the old days when we were smart with spies and treason, right? We used to handle it a little differently than we do now.”

ABC News’ Mariam Khan, John Parkinson, Benjamin Siegel and Chris Donovan contributed reporting to this article.