The first public presidential impeachment hearing in over 20 years is set to be held before the House Intelligence Committee on Wednesday, with witnesses Democrats believe will bring to life allegations that President Donald Trump has abused the power of the presidency.

The witnesses will emphasize the "simple abuse of power case" and illustrate the damage that abuse has caused, multiple sources have told NBC News. Republican lawmakers are expected to focus on the witnesses' lack of direct interaction with the president while giving credence to a debunked conspiracy theory that it was Ukraine and not Russia that meddled in the 2016 presidential election.

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When does the hearing start?

The hearing is set to start at 10 a.m. Wednesday. House Intelligence Committee Chairman Adam Schiff, D-Calif., will make an opening statement, followed by an opening statement by the ranking Republican on the committee, Rep. Devin Nunes of California, and then statements from the two witnesses.

Who's testifying?

The witnesses testifying Wednesday are Bill Taylor, the Trump administration's top diplomat in Ukraine, and George Kent, deputy assistant secretary of state for European and Eurasian affairs.

In his closed-door deposition, Taylorsaid he threatened to quit after he was told Trump was withholding hundreds of millions of dollars in aid to Ukraine because he wanted "investigations." He texted another diplomat that "it's crazy to withhold security assistance for help with a political campaign."

Kent told investigators in his deposition that he'd raised concerns that Trump lawyer Rudy Giuliani was poisoning Ukraine policy with "a campaign of lies" — and was warned to "lay low" by his boss afterward.

The two will testify together side-by-side at the witness table.

Who's doing the questioning?

Schiff and Nunes will have 45 minutes each to question witnesses in the first part of the hearing. They can also delegate the questioning to a committee lawyer instead, which Schiff has indicated he'll do.

Schiff will determine if there is a need for an additional 90 minute staff round or to move on to lawmaker questions.

Once the staff question round or rounds conclude, the format will revert to one similar to a traditional congressional hearing, with lawmakers getting five minutes each to ask questions.

Who's on the committee?

There are 13 Democrats and nine Republicans. The Democrats include Schiff, former presidential candidate Eric Swalwell of California and Joaquin Castro of Texas, the brother of presidential candidate Julián Castro. The other Democrats are Jim Himes of Connecticut, Terri Sewell of Alabama, Andre Carson of Indiana, Jackie Speier of California, Mike Quigley of Illinois, Denny Heck of Washington, Peter Welch of Vermont, Sean Patrick Maloney of New York, Val Demings of Florida and Raja Krishnamoorthi of Illinois.

On the Republican side are top Trump allies Nunes, John Ratcliffe of Texas and Jim Jordan of Ohio, who was added to the committee just last week. Also on the Republican side are Michael Turner and Brad Wenstrup of Ohio, Chris Stewart of Utah and Elise Stefanik of New York. Rounding out the roster are Mike Conaway and sometimes-Trump critic Will Hurd of Texas, both of whom have announced they are not running for re-election.

The hearing is set to take place in the House Ways and Means Committee hearing room because the Intelligence Committee doesn't have its own hearing room. The room is the same one where Hillary Clinton testified before the Benghazi Committee for more than eight hours in 2015.

What to expect from each side

Himes told Chuck Todd on Sunday's "Meet the Press" that the public will "hear immensely patriotic, beautifully articulate people telling the story of a president who ... extorted a vulnerable country by holding up military aid."

Republicans are likely to focus on the fact that much of Taylor and Kent's information about what Trump was and was not doing came from other people, not from their direct interactions with the president. Some of those people — including acting White House chief of staff Mick Mulvaney and former national security adviser John Bolton — have refused to cooperate with the probe.

Republicans are also expected to stress that it's not believed that Ukrainian President Volodymyr Zelenskiy was aware that Trump had placed a hold on almost $400 million in aid to his country during their July 25 phone conversation. During Taylor's deposition, which was released to the public last week, Nunes also used his questioning to suggest that Ukraine was behind the hacking of the Democratic National Committee and not Russia, the country U.S. intelligence agencies have unanimously agreed was the culprit.

How long will the hearing take?

TBD, but it's expected to wrap up between 2:30 and 4:30 p.m., barring any extra questioning or Republican stalling tactics.

Where can you watch?

NBC News will air a special report at 10 a.m. ET led by "NBC Nightly News anchor" Lester Holt, NBC News chief legal correspondent Savannah Guthrie and NBC News political director Chuck Todd. MSNBC will anchor special coverage hosted by "The 11th Hour" host Brian Williams and "Deadline: White House" host Nicolle Wallace.

The hearings will be streamed live on NBC News NOW, NBCNews.com and MSNBC.com. NBCnews.com will also feature a live blog with contributors from across NBC News with news, fact checks and analysis. The coverage will be collected at NBCNews.com/impeachment.

Are more hearings scheduled?

Former Ukraine Ambassador Marie Yovanovitch is scheduled to testify before the same committee on Friday. Schiff said in a letter to his colleagues Tuesday that additional witnesses will be announced by the end of the week.