Even as House Democrats were announcing their Ukraine-related impeachment articles against President Trump on Tuesday, a key Ukrainian witness was calling into question a central piece of that puzzle.

But skepticism of his account is warranted.

Andriy Yermak is the top aide to Ukrainian President Volodymyr Zelensky who was regularly in touch with Trump aides, and he spoke with Time magazine in a new interview. The news: He questions a key claim that one of those aides told him there was a quid pro quo involving military aid.

That was what Gordon Sondland, the U.S. ambassador to the European Union, testified that he told Yermak on Sept. 1 in Warsaw, but Yermak denies it. He said that Sondland didn’t actually pull him aside and that their discussion was much more superficial.

“Gordon and I were never alone together,” Yermak told Time’s Simon Shuster. “We bumped into each other in the hallway next to the escalator, as I was walking out.”

Yermak added: “And I remember — everything is fine with my memory — we talked about how well the meeting went. That’s all we talked about.”

This would be significant because, although there were plenty of instances of a White House meeting being tied to the investigations, this is the one confirmation that a quid pro quo was also communicated to Ukraine specifically on the military aid. Sondland said, “I told Mr. Yermak that I believed that the resumption of U.S. aid would likely not occur until Ukraine took some kind of action on the public statement that we had been discussing for many weeks.”

If that didn’t happen, that portion of Democrats’ impeachment case becomes much more tenuous. And there is already uncertainty about when Ukraine even became aware that the military aid was being withheld. (If Ukraine didn’t even know it was being withheld, the argument goes, how could it have been intended as leverage?)

The first thing we can say is that it’s not out of the question that Sondland would get something off in his testimony. It has happened before, after all, and this interaction is already something that he had amended in his later testimony.

But Sondland isn’t the only person who testified to this. So did former White House aide Tim Morrison, who said that he saw Sondland pull Yermak aside and that Sondland told him about the content of the conversation in real time.

Here’s the relevant portion of Morrison’s testimony:

Q: During the Warsaw visit Ambassador Sondland, I guess, had a sidebar with Yermak?
MORRISON: Yes. Ukrainian Presidential Adviser Yermak.
Q: Did you witness that exchange?
MORRISON: I witnessed it, yes.
Q: Okay. And were you part of the exchange on did you just see it occur?
MORRISON: I saw it occur.
Q: Okay. And what did you learn about that exchange? I guess Ambassador Sondland told you what he told Yermak?
MORRISON: He came -- he essentially walked across a, you know, a -- I don’t know how to describe the room. He walked across the space and he briefed me on what he said he had said to Mn. Yermak.
Q: Okay. What did he tell you?
MORRISON: He told me that in his -- that what he communicated was that he believed the -- what could help them move the aid was if the prosecutor general would go to the mike and announce that he was opening the Burisma investigation.

So there are two witnesses, under oath and penalty of perjury, who are testifying to this, including Morrison, who was a Republican witness and wasn’t eager to accuse Trump of wrongdoing. And it’s their word against that of a witness who wasn’t under oath.

It’s also worth noting that Ukraine has plenty of motivation to cast doubt on this, and that some of Yermak’s comments strain credulity.

Ukrainians have tried to avoid accusing Trump and his aides of leveraging them, with Zelensky maintaining that he felt no pressure from Trump. This, though, isn’t all that surprising, given that Ukraine relies on the United States for military aid and more. Feeding the case against Trump means alienating the man who will be U.S. president for another year and possibly four more beyond that. What’s more, the idea that Trump requesting investigations wouldn’t connote any pressure whatsoever, given the power imbalance between the countries, is pretty far-fetched.

Even more than that, though, Yermak’s version is rather Pollyannaish. He suggests that, even when Ukraine learned about the frozen aid, it didn’t necessarily connect it to the investigations.

“We never had that feeling,” he said. “We had a clear understanding that the aid has been frozen. We honestly said, ‘Okay, that’s bad, what’s going on here?’ We were told that they would figure it out. And after a certain amount of time, the aid was unfrozen. We did not have the feeling that this aid was connected to any one specific issue.”

It bears emphasizing that Yermak was the one most intimately familiar with the horse trading that was going on. His texts with Trump aides regularly attached a White House meeting for Zelensky to Ukraine announcing the investigations. To read those texts and not believe there was at least an implied quid pro quo is to put blinders on.

To hear Yermak tell it, he was involved in all of those quid-pro-quo-y discussions, but when the military aid was frozen, he didn’t think that might be related to the investigations that still hadn’t been announced. If he didn’t, he was really giving the benefit of the doubt to a bunch of people who were rather clearly leveraging him.

Yermak’s account is a worthwhile data point. As with Zelensky’s comments, though, it’s worth considering where it’s coming from — and the cost of saying anything else.