House Democrats are set to close their second week of public impeachment hearings Thursday with testimony from two witnesses expected to detail events inside the White House and a key conversation involving President Trump.

Scheduled to appear are Fiona Hill, the well-known Russia expert who served until this summer as a top director on the National Security Council; and foreign service officer David Holmes, the political counselor at the U.S. Embassy in Kyiv.

The hearing is scheduled to convene at 9 a.m. ET and will appear live here.

Dr. Hill

Hill is expected to tell lawmakers about the concerns she had with the merits of the Ukraine affair, in which Trump sought concessions from Ukraine's president in exchange for engagement and continued financial assistance that had been authorized by Congress.

The U.S. had been sending aid to Ukraine since it was invaded by Russia in 2014 to help its military against Russian and Russian-backed forces still operating in the east.

The national security establishment opposed the freeze of that aid for several weeks this summer.

Hill told impeachment investigators in her closed deposition that she resented the smear campaign run against the former U.S. ambassador to Ukraine Marie Yovanovitch by Trump's personal lawyer Rudy Giuliani.

Hill also is a key witness about the former national security adviser, John Bolton, who has been described as an important player in the Ukraine saga but from whom Congress has not heard directly.

Bolton, per Hill, warned about the "drug deal" being cooked up by Trump's deputies with Ukraine and about the role played by Giuliani, whom Hill said Bolton called a "hand grenade that is going to blow everybody up."

Mr. Holmes

Holmes is a diplomatic staffer who went to lunch in July in Kyiv with the ambassador to the European Union, Gordon Sondland.

During that encounter, Sondland called Trump on his mobile phone to talk about the "investigations" that Trump wanted from his Ukrainian counterpart, Volodymyr Zelenskiy.

Sondland appeared on Wednesday in a threshold moment within the Ukraine affair.

He didn't dispute much of what Holmes has told investigators about the episode, but there was one key discrepancy — over a which specific words he used.

Holmes said in his deposition that Sondland told him Trump only cared about "big stuff" that affected him, like what Holmes called the "Biden investigation" Trump wanted from Ukraine.

Sondland says he didn't know in real time that the investigation connected with the word "Burisma" — a Ukrainian company that for a time paid the son of former Vice President Joe Biden — was, in effect, code for the Biden family.

Members of Congress asked Sondland about this on Wednesday. He said that while he doesn't dispute much of what Holmes has said, he disputes having used the term "Biden."

Sondland said that if he had the full picture then of what's since become clear, he wouldn't have gone along with a policy he now says he considers inappropriate.

Impeachment investigators on Thursday likely will press Holmes to square his recollection with that of Sondland.

What comes next?

One question raised by the Thursday session — and not yet answered definitively by Democrats — is whether it will be the last.

House Intelligence Committee Chairman Adam Schiff, D-Calif., who has been leading this phase of the impeachment inquiry, hasn't said definitively whether the hearing would end his portion of the process.

That matters because it affects the timing of the balance of Democrats' putative impeachment program: Once Schiff's panel concludes its work, action could then shift to the House Judiciary Committee, which would need to initiate and advance articles of impeachment to the full House.

Neither Schiff nor House Speaker Nancy Pelosi, D-Calif., have committed to a timetable and have suggested impeachment, in fact, isn't a foregone conclusion but would depend on Schiff's investigation.

If that investigation concludes on Thursday, and Democrats decide to move ahead, the next act could open in this drama.

If Schiff says on Thursday that he intends to depose more witnesses or convene more hearings, that would push potential successive events forward, potentially to Christmas or beyond.

And if Trump were impeached in the House, that would trigger a trial in the Senate — one that Senate Majority Leader Mitch McConnell, R-Ky., said this week that he's convinced Trump would win.