WASHINGTON (AP) — House Democrats are giving President Donald Trump a reality show for the ages as they take their case public for his impeachment.

But the proceedings are much more than showbiz, with lawmakers considering the use of a grave and seldom-employed power spelled out in the Constitution.

With the bang of a gavel, House Intelligence Committee Chairman Adam Schiff will open the impeachment hearings Wednesday into Trump's pressure on Ukraine to investigate Democratic rival Joe Biden's family. Big questions loom, including how strongly officials connected what Trump called that "favor" to U.S. military aid to Ukraine.

Impeachable offenses? Worthy of Trump's removal? And critically, will a pair of diplomats and their accounts nudge more Americans behind impeaching the nation's 45th president ?

It's all unfolding at 10 a.m. in a pillared House chamber, in the shadow of the 2020 presidential and congressional elections.

Here's what to know:

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WHO'S UP FIRST?

Shortly after Schiff's gavel, he and ranking Republican Devin Nunes will begin the questioning. They get 45 minutes each, or designate staff attorneys to do so.

Members of the panel will then get five minutes each to ask questions, alternating between Republicans and Democrats.

There will also be exhibits. Democrats at least, are expected to display excerpts from transcripts, text messages, relevant news articles and social media posts.

The goal is to shutter the hearing by 4:30 p.m.

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KNOW THIS

"The President, Vice President and all civil officers of the United States, shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors."

Expect numerous mentions of Article 2, Section 4 of the Constitution , especially on whether Trump's own words and actions meet the vague threshold of "high crimes and misdemeanors." Some Democrats and diplomats say conditioning U.S. aid on whether Ukraine goes after Biden's son, Hunter, sounds like "bribery." Republicans deny that, saying Trump did not explicitly offer aid for the Biden probe.

What it's not: A trial, which would be conducted by the Senate if the House approves articles of impeachment. So no matter what the president tweets , he is not entitled to a defense attorney.

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...AND THIS

It's only the fourth time in American history that Congress has launched impeachment proceedings against a sitting president. Two of those — against Andrew Johnson in 1868 and Bill Clinton 130 years later— resulted in their impeachments, or formal charges approved by the House. Both were acquitted by the Senate.

Former President Richard Nixon resigned in 1974 before the House could vote to impeach him.

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THE SPARK

A whistleblower's complaint about Trump's July 25 telephone call with Ukrainian President Volodymyr Zelenskiy ignited the impeachment investigation. Trump responded on Sept. 24 by releasing a rough transcript.

During the hearing Wednesday, listen for discussion about a key exchange during that 30-minute call , in which Zelenskiy invokes the still blocked military aid and the U.S. president responds:

"I would like you to do us a favor though." Trump then asks Zelenskiy to investigate a debunked conspiracy theory about the 2016 election, and later explicitly mentions the Bidens.

Trump says the call was "perfect" and contained no "quid pro quo," or this for that.

Democrats say it shows Trump using his office to pressure a foreign government to help him politically.

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IN THE ROOM

The enormous hearing room in the Longworth House Office Building has a storied history. It's normally where the powerful House Ways and Means Committee works on taxation issues.

But it's also where former FBI Director James Comey in 2017 repudiated Trump's unfounded claim about being wiretapped during the election. Former first lady Hillary Clinton also sat at the witness table in 1993 to testify about her ultimately doomed effort to rewrite the nation's health care laws.

And seven decades ago, the full House met there while the chamber in the Capitol across the street was renovated.

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'INVESTIGATIONS, BIDEN and CLINTON'

Democrats chose Ambassador William "Bill" Taylor and career Foreign Service officer George Kent to start the storytelling of public hearings. They will describe a parallel foreign policy toward Ukraine led by Trump's personal attorney, Rudy Giuliani, and other White House officials.

"I discovered a weird combination of encouraging, confusing and ultimately alarming circumstances," Taylor testified in an Oct. 22 statement. He is a West Point graduate and Vietnam War veteran who has served under every presidential administration, Republican and Democrat, since 1985, and also worked for then-Sen. Bill Bradley, D-N.J.

Kent, the bow-tie wearing career foreign service officer, testified on Oct. 15 there were three words Trump wanted to hear from the Ukraine president: "Investigations, Biden and Clinton."

He also told the investigators about the "campaign of lies" against former U.S. ambassador to Ukraine, Marie Yovanovitch that he said was waged by Giuliani and contributed to her being recalled from the position.

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THE RINGER

Republicans have put House Rep. Jim Jordan on the Intelligence Committee. Though Nunes is the senior Republican, look for the congressman from Ohio to act as an especially fierce attacker of the witnesses' credibility and the Democrats' case for impeachment.

At its heart, the GOP argument is that the impeachment effort is unfair and sparked because "unelected and anonymous bureaucrats disagreed" with Trump's decisions on Ukraine.

Some Republicans have urged the outing of the whistleblower.

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WHAT AMERICANS THINK NOW

An AP-NORC Center poll conducted in late October found Americans more approving than disapproving of the impeachment inquiry, 47% to 38%.

Even in the throes of impeachment, approval of the president's job performance has not changed significantly.

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NEXT UP

Yovanovitch testifies Friday.

She has twice served as an ambassador — to the Kyrgyz Republic and to Armenia — before being confirmed as the U.S. ambassador to Ukraine in a Senate voice vote in July 2016.

Seen as a tough ambassador, at a time when the U.S. was trying to root out corruption in the young democracy, she was recalled from Ukraine by Trump last spring.

Known as Masha, Yovanovitch testified on Oct. 11 that she was told that people were "looking to hurt" her.

More hearings are expected next week.

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Follow Kellman at http://www.twitter.com//APLaurieKellman

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Associated Press researcher Randy Herschaft and Hannah Fingerhut contributed to this report.