On Tuesday, former diplomat Kurt Volker is publicly testifying in the impeachment inquiry about his role as one of Trump’s point people negotiating with Ukraine.

Who he is

Volker was the State Department’s special envoy to Ukraine until he resigned abruptly the weekend before his private deposition in the impeachment inquiry.

Why he matters

He was one of three men designated by Trump to steer Ukraine policy. Volker, European Union Ambassador Gordon Sondland, and Energy Secretary Rick Perry dubbed themselves the “three amigos.” Other diplomats such as the acting ambassador to Ukraine said the trio formed the core of an underground diplomatic channel on Ukraine that usurped the regular diplomatic channel and at times ran counter to U.S. interests.

Volker was one of the first in this group willing to testify to Congress, and he testified that he knew Trump’s personal lawyer Rudolph W. Giuliani was pushing unsubstantiated theories about former vice president Joe Biden in Ukraine.

What we learned from his private testimony

Volker said he didn’t like working with Giuliani but knew he had to. To that end, he handed Congress text messages between the “three amigos,” Giuliani and a senior official in Ukraine that show the Americans asking for investigations in exchange for a meeting with Trump. “Most impt is for Zelensky to say that he will help investigation,” Volker texted his American colleagues at one point, referring to Ukrainian President Volodymyr Zelensky.

Here’s another eyebrow-raising text he sent to an Ukrainian official: “assuming President Z convinces trump he will investigate / ‘get to the bottom of what happened’ in 2016, we will nail down date for visit to Washington.”

Volker also testified that even though he engaged regularly with Giuliani, he was suspicious of Giuliani and tried to warn him off some conspiracy theories about Ukraine, though they eventually made their way to Trump.

Key quote from his private testimony

“I believe that Giuliani was interested in Biden, Vice President Biden’s son [Hunter],” Volker said.

What he doesn’t say in his private testimony

That there was an explicit quid pro quo, at least not one he knew of. Though other diplomats have testified that Volker said he was going to tell Ukraine’s president what he needed to do to get a White House meeting.

What to watch for in his public testimony

Volker’s testimony was at odds with those of several key officials who sketched out a clear quid pro quo of aid and an Oval Office meeting for investigations. Volker could face intense pressure to amend his remarks or change his story.

Greg Jaffe contributed to this article.