After Bill Taylor testified last week to multiple corrupt quid pro quos between the Trump team and Ukraine, President Trump attacked him as a “Never Trumper.” He did so despite the fact that Taylor, the top U.S. diplomat in Ukraine, was selected for his job just a few months ago by Secretary of State Mike Pompeo.

Good luck trying to pull that with the latest big witness.

Lt. Col. Alexander S. Vindman will become the latest official Tuesday to testify to a corrupt quid pro quo. And he might be the most significant to date, given his profile and his proximity to some of the key events.

According to his prepared testimony, Vindman will say that European Union Ambassador Gordon Sondland said after a July 10 meeting with a top Ukrainian official that a long-sought meeting between Ukrainian President Volodymyr Zelensky and Trump depended upon Ukraine launching specific investigations — those involving former vice president Joe Biden and his son Hunter Biden, as well as a conspiracy theory about the origins of the investigation of Russian interference in the 2016 U.S. election:

Amb. Sondland started to speak about Ukraine delivering specific investigations in order to secure the meeting with the President, at which time [National Security Adviser John] Bolton cut the meeting with [top Ukraine official Oleksandr Danylyuk] short. Following this meeting, there was a scheduled debriefing during which Amb. Sondland emphasized the importance that Ukraine deliver the investigations into the 2016 election, the Bidens, and Burisma.

Vindman adds that he raised concerns about the arrangement — both immediately to Sondland and twice to a top National Security Council lawyer.

“I stated to Amb. Sondland that his statements were inappropriate, that the request to investigate Biden and his son had nothing to do with national security, and that such investigations were not something the NSC was going to get involved in or push,” Vindman says.

Vindman says elsewhere in his testimony that he didn’t just think the arrangement was wrong, but that he viewed it as harmful to U.S. foreign policy.

“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,” he says.

Vindman is the fifth person to say there was a quid pro quo. Along with Taylor, Sondland reportedly admitted to some kind of quid pro quo in his testimony, acting White House chief of staff Mick Mulvaney admitted to one publicly before walking back his comments, and Sen. Ron Johnson (R-Wis.) indicated there was one in public interviews.

Here’s why Vindman is different than the others, though: In addition to delivering it in sworn testimony, that testimony is the first by a White House official who was on the July 25 call between Trump and Zelensky. His opening statement doesn’t dwell on that call too much — he does say, “This would all undermine U.S. national security” — but that gives you a sense of how close to these decisions and conversations he was.

By contrast, Taylor’s most significant allegation is secondhand, relying upon another official telling him that Sondland had conveyed the quid pro quo to a top Ukrainian official. (We’re still waiting for the testimony of that official, Tim Morrison.) And Sondland seemed to be putting a good face on whatever quid pro quo existed.

Vindman’s profile also reads like someone who was almost crafted to be an unassailable witness. He was born in the Soviet Union, meaning he’s someone who would seem to have a genuine interest in the stability of the region. He has been a U.S. military officer and diplomat for more than two decades, serving under both Democratic and Republican presidents. He also served in combat operations in Iraq and was injured in an IED attack, receiving a Purple Heart. And as Philip Bump reported Tuesday morning, as a child he was even featured in Ken Burns’s documentary, “America,” talking about the Statue of Liberty.

Lt. Col. Alexander S. Vindman is briefly interviewed in Ken Burns’s 1985 film, “Statue of Liberty.” (Ken Burns UNUM/Florentine Films)

As with Taylor, of course, that doesn’t mean Trump’s supporters won’t try to attack Vindman. (We’ve been here before with Robert Mueller, John McCain and Khizr Khan.) It even began on Monday night, after the New York Times first reported on his impending testimony.

Fox News host Laura Ingraham noted that the Times reported Ukraine sought advice from Vindman on how to deal with Trump’s personal lawyer, Rudolph W. Giuliani, because Vindman is fluent in their language.

“Here we have a U.S. national security official who is advising Ukraine, while working inside the White House, apparently against the president’s interest, and usually, they spoke in English,” she said. “Isn’t that kind of an interesting angle on this story?!”

John Yoo, a veteran of the Justice Department under President George W. Bush, then took that ball and ran with it. He called it “astounding” and added, “You know, some people might call that espionage,” according to the Daily Beast.

Then on CNN on Tuesday morning, former congressman Sean Duffy (R-Wis.) suggested Vindman’s loyalty might lie with Ukraine.

“He has an affinity, probably, for his homeland," Duffy said, adding: “I read his statement ... and it seems very clear that he is incredibly concerned about Ukrainian defense. I don’t know that he’s concerned about American policy, but his main missions was to make sure that the Ukraine got those weapons.”

The problem for people like Yoo, Ingraham and Duffy is that, even if you set aside the optics of attacking a Purple Heart recipient, Vindman is merely the latest to testify to a direct link between these specific investigations and official favors for the Ukrainian government — whether the favor was a meeting or the release of hundreds of million of dollars in military aid. There appear to be lots and lots of people who were at least tangentially aware of this, and now we have firsthand witnesses testifying to it as well.

They can certainly try to knock each and every witness down, but it’s going to become more and more difficult as more and more people step forward.

And when you have to start attacking the Purple Heart guy, you know you’re in a bad spot.

This post has been updated.