HUNTER BIDEN: George Kent Details Hunter Biden in Opening Statement

In a pillared House chamber at 10 a.m. ET on Wednesday, in the shadow of the 2020 presidential and congressional elections, House Democrats are set to host the first public hearing involving the potential impeachment of a president since November 19, 1998 -- and, they insist, they aren't happy about it.

"It’s a sad day," House Speaker Nancy Pelosi, D-Calif, told Fox News on Tuesday. "A calm day. A prayerful day." For his part, House Intelligence Committee Chairman Adam Schiff, D-Calif., called the hearings a "solemn undertaking" in a letter to colleagues.

Behind the scenes, House Democrats were predicting a "phenomenal week," Fox News is told. At the same time, Republicans have been preparing a methodical and vigorous cross-examination of Democrats' witnesses, whose accounts of President Trump's alleged wrongdoing have been based largely on hearsay and intuition.

Capitol Hill security officials told Fox News they're not anticipating the kinds of organized protests that rocked the Supreme Court confirmation hearings of Brett Kavanaugh last year, but sources on both sides of the aisle have cautioned that the day will be unpredictable. The proceedings are to be held in the cavernous House Ways and Means Committee hearing room at the Longworth House Office Building.

With the bang of a gavel, Schiff will open the impeachment hearings Wednesday into Trump's alleged pressure on Ukraine to investigate 2020 presidential candidate Joe Biden's dealings in the country. The former vice president, a Democrat, has boasted about pressuring Ukraine to fire its top prosecutor, as his son Hunter Biden held a lucrative role board of a Ukrainian natural gas company despite having little relevant expertise.

A whistleblower's complaint about Trump's July 25 telephone call with Ukrainian President Volodymyr Zelensky ignited the impeachment investigation. During the hearing Wednesday, a key exchange during that 30-minute call, which has been outlined in a Sept. 24 transcript released by the White House, could take center stage. Zelensky has said he felt no pressure during the call.

"I would like you to do us a favor though," Trump said at one point in the call, after a mention of U.S. military aid to Ukraine. Ukraine apparently was not aware that the U.S. was withholding new military aid until August, approximately two weeks before the U.S. ultimately released the aid and well after Trump's phone call with Zelensky.