On Wednesday, diplomat Gordon Sondland is publicly testifying in the impeachment inquiry about his work negotiating with Ukrainians to launch investigations into President Trump’s political rivals. He is one of the most crucial witnesses, in that he could be the witness who can link a quid pro quo directly to Trump.

Who he is

He’s a Trump campaign donor who was rewarded with a cushy job as the U.S. ambassador to the European Union. He’s always wanted to be an ambassador, and by embracing Trump, he found a way to become one.

Why he matters

Sondland is one of the few witnesses in the impeachment inquiry who may be in a position to confirm what Trump wanted out of Ukraine in exchange for holding up its military aid. He is one of three political appointees chosen by Trump to drive his unofficial Ukraine policy (they called themselves the “three amigos”), and he appears to have worked closely with Trump throughout this summer on this. A former senior national security official, Tim Morrison, testified he knew Sondland talked to Trump about a half-dozen times this summer as the White House froze aid to Ukraine. Sondland traveled to Ukraine at Trump’s request, despite not having Ukraine in his diplomatic portfolio. He attended key Oval Office meetings with Trump about Ukraine.

One vivid example of how closely Sondland was involved in these negotiations: The day after Trump called Ukraine’s president in July, Sondland was in Ukraine. He called the president on an open line cellphone from a restaurant to relay to the president that Ukraine would launch “investigations,” according to a U.S. Embassy worker who saw and overheard the conversation.

“Sondland will address any issues that arise from this in his testimony next week,” his lawyer said in response to the revelation of that cellphone call.

What we learned from his private testimony

Sondland was one of the first witnesses to appear before Congress and made a bunch of “I don’t recall” statements. But after other State Department and White House officials pointed the finger at Sondland as the one communicating the quid pro quo to Ukrainians, Sondland issued a clarification to his testimony saying he subsequently recalled what he told the Ukrainians.

He acknowledged in his revised testimony that he communicated to the Ukrainians: Military aid for announcing an investigation into Democrats. Though he dubiously testified he didn’t realize having Ukraine investigate “Burisma” was code for “Joe Biden."

Key quote from his (revised) private testimony

“I presumed that the aid suspension had become linked to the proposed anti-corruption statement.”

That’s Sondland explaining why he told Ukrainians they had to announce investigations into Trump’s political rivals to get their military aid unfrozen by the Trump administration. It’s the clearest statement yet that there was a quid pro quo, even if Sondland himself rejects that term.

What to watch for in his public testimony

Sondland could be the person who links that quid pro quo directly to Trump. Sondland testified that he “presumed” the frozen aid was linked to investigations Trump wanted, and so he told the Ukrainians as much. Was he just acting of his own volition? Was someone else telling him what to do?