This post has been updated with his public testimony.

Democrats specifically chose him as one of their first witnesses, along with George Kent, to tell the story of President Trump and Ukraine, and we can see why. As the top U.S. diplomat in Ukraine, Taylor had a unique vantage point: Key figures in pushing Trump’s Ukraine policy were open with him as they tried to get Ukraine to do Trump’s bidding.

Who he is

Taylor is the acting U.S. ambassador to Ukraine, also known as the chargé d’affaires. He is also a career diplomat and military veteran who has served in Republican and Democratic administrations, including as ambassador to Ukraine from 2006 to 2009. He was asked by Secretary of State Mike Pompeo to take over after Trump had Marie Yovanovitch removed from the ambassadorship. He said it was a tough decision to return to Kyiv — the treatment of Yovanovitch and Trump’s personal attorney Rudolph W. Giuliani’s involvement were among the factors that gave him pause — but ultimately he accepted Pompeo’s request.

Why he matters

Taylor took over as the top U.S. official in Ukraine as this scandal was unfolding. He wasn’t in the room where the alleged quid pro quo orders were issued, but he was talking to many people who were in the key rooms both in Washington and in Kyiv.

What we learned from his public testimony

Taylor testified that he learned via conversations with White House aides, national security officials and Trump’s point people in Ukraine that there was a concerted effort to force Ukraine into a quid pro quo: If the country wanted military aid and an Oval Office meeting, its president needed to publicly agree to investigate Democrats. What’s critical about Taylor’s testimony is that he didn’t attribute this to one conversation with one person. Over the course of several months, he talked to high-level officials at the National Security Council, officials in Ukraine’s presidential office and two of the “three amigos” designated by Trump to handle Ukraine policy outside the normal diplomatic channels. “I was in the regular channel” of diplomacy, Taylor testified, “but I was also in the irregular one.”

Taylor’s testimony has been corroborated by others, including National Security Council official Tim Morrison, and has forced a Trump ally to revise his. Gordon Sondland, the U.S. ambassador to the European Union, originally testified that he didn’t remember offering Ukraine a quid pro quo to unfreeze its military aid. But Sondland later told Congress that he had “refreshed my recollection” after reading testimony by Taylor and Morrison, and confirmed that he did tell Ukrainians that military aid would probably be held until they agreed to investigate Democrats.

Key quote from Taylor’s private testimony

Holding up security aid, like Trump did, “for no good policy reason, no good substantive reason, no good national security reason, is wrong.”

Note Taylor said it’s wrong regardless of whether Trump tried to get something for it — even though Taylor is convinced Trump’s White House used aid to try to get investigations into his political opponents.

What he didn’t say in his public or private testimony

He couldn’t conclusively say Trump directed all of this. He said he knows Sondland told the Ukrainians that there was a quid pro quo: military aid for investigations. He also testified that one of his staff members overheard Trump asking Sondland about “the investigations,” but that’s as much as he knows about Trump’s involvement. Here’s an exchange Taylor had with House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) in which Taylor noticeably declines to implicate Trump as Schiff does:

SCHIFF: At the time they found out, they knew what President Trump wanted from them, that he wanted these investigations, correct?
TAYLOR: Ambassador Sondland informed [Ukrainian President Volodymyr] Zelensky’s staff, that is Mr. [Andriy] Yermak, of what was required, yes.
SCHIFF: So Ukraine finds out about the hold, you’re not able to give them a reason for the hold. No one is able to give them a reason for the hold. They know the president wants these investigations. And then they’re told in Warsaw by Ambassador Sondland essentially, ‘You’re not getting the aid unless you do the investigations,' correct?
TAYLOR: That’s correct.