On Thursday, a former top Russia expert for the White House, Fiona Hill, is testifying publicly in the impeachment inquiry about why she and other national security officials were concerned about what people in President Trump’s orbit were telling Ukrainians.

Who she is

Hill was the White House’s top expert on Russia. Her official title was senior director for Europe and Russia on the National Security Council, which is in the White House. She was Lt. Col. Alexander Vindman’s supervisor, and she was succeeded in her position by Tim Morrison. Both Morrison and Vindman testified Tuesday. She is also a former senior U.S. intelligence official and Russia scholar, and an author of a respected biography of Russian President Vladimir Putin. She is a British-born naturalized citizen.

Why she matters

Hill is important because she witnessed or heard about key early events, including a July 10 meeting between national security officials, Trump’s point person on Ukraine and Ukrainian officials at the White House. But she also is a proxy for one of the people Democrats most want to testify: former national security adviser John Bolton. She reported to him directly.

Why Bolton matters

Hill and other officials have testified that Bolton was quite upset about how Trump’s personal lawyer, Rudolph W. Giuliani, and one of Trump’s point people on Ukraine, European Union Ambassador Gordon Sondland, were handling Ukraine policy and usurping the national security and diplomat apparatus. Bolton would be one of the highest-level officials to testify, someone who regularly talked to Trump. He would confirm other witnesses’ accounts about what he heard and share some of his own conversations with Trump, report The Washington Post’s Carl Leonnig and Tom Hamburger.

But Bolton is not scheduled to testify yet. Even though he no longer works for the White House, Bolton has said he can’t talk because of a White House ban on participating with the inquiry. He instead joined a lawsuit with another former deputy to ask the courts to decide which branch should win out in a battle on whether he talks: the White House or Congress. That lawsuit may take too long to resolve for Democrats’ timeline.

What we learned from her private testimony

Hill describes in detail two July 10 meetings at the White House where diplomat Sondland brought up to the Ukrainians investigations wanted by Trump. It alarmed national security officials. She said Bolton abruptly ended the meeting in his office with his Ukrainian counterpart after Sondland blurted out a reference to “the investigations.”

Hill then followed Sondland to a second meeting in the West Wing basement where she says he went even further. She heard Sondland say Ukraine’s president would get a meeting at the White House if he agreed to the investigations Trump wanted — including one into a company, Burisma, that had hired former vice president Joe Biden’s son Hunter Biden as a board member.

She said: “And Ambassador Sondland, in front of the Ukrainians, as I came in, was talking about how he had an agreement with Chief of Staff [Mick] Mulvaney for a meeting with the Ukrainians if they were going to go forward with investigations. And my director for Ukraine was looking completely alarmed. And I came in again as this discussion was underway.”

She also said when she read the rough transcript of Trump’s call with Ukraine’s president that she was “shocked” and “saddened” to see the way he disparaged former Ukraine ambassador Marie Yovanovitch, and that it was “pretty blatant” Trump was asking Ukraine to launch political investigations to get a meeting with him.

Key quote from her private testimony

“ … This is a direct quote from Ambassador Bolton: You go and tell [NSC lawyer John] Eisenberg that I am not part of whatever drug deal Sondland and Mulvaney are cooking up on this.”

What she didn’t say in her private testimony

Whether Trump was involved in any of this, beyond what we know he told Ukraine’s president in the phone call. Hill left her White House job July 19, days before the Trump-Zelensky call.

What to watch for in her public testimony

Hill has the ability to connect a lot of dots: She was present when Sondland appeared to offer Ukrainians a quid pro quo. She heard Sondland say Trump put him in charge of Ukraine and Trump’s chief of staff told him to ask for the investigations. She didn’t like the way Trump handled the Ukraine phone call nor Yovanovitch, and she has insight into what one of Trump’s top aides at the time, Bolton, thought about it all.

Greg Miller contributed to this report.