The White House announced in a fiery letter Sunday night that President Trump and his lawyers won't participate in the House Judiciary Committee’s first impeachment hearing scheduled for Wednesday -- even accusing the panel's Democratic chairman, Jerry Nadler, of "purposely" scheduling the proceedings when Trump would be attending the NATO Leaders' Meeting in London.

The five-page letter came as the Democratic majority on the House Intelligence Committee was preparing to approve a report on Tuesday that will outline possible charges of bribery or “high crimes and misdemeanors,” the constitutional standard for impeachment. After receiving the report, the Judiciary Committee would prepare actual charges.

“This baseless and highly partisan inquiry violates all past historical precedent, basic due process rights, and fundamental fairness,” wrote White House counsel Pat Cipollone, continuing the West Wing’s attack on the procedural form of the impeachment proceedings. Cipollone said Nadler provided only "vague" details about the hearing, and that unnamed academics -- and not "fact witnesses" -- would apparently be attending.

"As for the hearing scheduled for December 4, we cannot fairly be expected to participate in a hearing while the witnesses are yet to be named and while it remains unclear whether the Judiciary Committee will afford the president a fair process through additional hearings," Cipollone said. "More importantly, an invitation to an academic discussion with law professors does not begin to provide the President with any semblance of a fair process. Accordingly, under the current circumstances, we do not intend to participate in your Wednesday hearing."

He continued: "When the Judiciary Committee scheduled a similar hearing during the Clinton impeachment process, it allowed those questioning the witnesses two-and-a-half weeks' notice to prepare, and it scheduled the hearing on a date suggested by the president's attorneys. Today, by contrast, you have afforded the president no scheduling input, no meaningful information and so little time to prepare that you have effectively denied the administration a fair opportunity to participate."

READ THE FULL WHITE HOUSE LETTER

Cipollone's letter made clear that his response applied only to the Wednesday hearing, at least for now. Cipollone demanded more information from Democrats on how they intended to conduct further hearings before Trump would decide whether to participate in those hearings, amid sagging national support for Democrats' probe.

Specifically, Cipollone demanded to know whether Republicans would be able to cross-examine and call their own fact witnesses, including House Intelligence Committee Chairman Adam Schiff, D-Calif.

House-passed rules provide the president and his attorneys the right to cross-examine witnesses and review evidence before the committee, but little ability to bring forward witnesses of their own.

"If [Schiff] chooses not to (testify), then I really question his veracity in what he’s putting in his report,” said Rep. Doug Collins, the top Republican on the Judiciary Committee. "It’s easy to hide behind a report," Collins added. "But it’s going to be another thing to actually get up and have to answer questions.”

Schiff has come under scrutiny from Republicans, in part because of his overtly partisan comments and his previous claim in a televised interview that "we have not spoken directly with the whistleblower." A Schiff spokesperson later narrowed that claim in October, telling Fox News that Schiff himself "does not know the identity of the whistleblower, and has not met with or spoken with the whistleblower or their counsel" for any reason.

STATE DEPT OFFICIAL TESTIFIES THAT HE FLAGGED BIDEN CONFLICT OF INTEREST ISSUES -- BUT WAS TOLD NOW'S NOT THE TIME

An aide to Schiff insisted that when Schiff mentioned "we" had not spoken to the whistleblower, he was referring to members of the full House intelligence committee, rather than staff. NBC National Security reporter Ken Dilanian flagged Schiff's explanation as "deceptive" late Wednesday, and Schiff acknowledged he "should have been more clear" concerning whistleblower contacts.

The panel of constitutional scholars who will testify on Wednesday will weigh in on the question of whether the president committed an impeachable offense by allegedly withholding of military aid to Ukraine until it investigated former Vice President Joe Biden.

During impeachment hearings last month, a career State Department official testified that in January or February 2015, he "became aware that [Joe Biden's son] Hunter Biden was on the board" of Ukrainian company Burisma Holdings while his father Joe Biden was overseeing Ukraine policy as vice president -- and that he raised concerns about potential conflicts of interest at the time. Joe Biden has openly bragged about pressuring Ukraine to fire its top prosecutor by threatening to withhold $1 billion in critical U.S. aid., all while Burisma was under scrutiny.

Republicans had urged President Trump not to attend the Democrats' hearings, arguing that his presence would validate a process they have repeatedly derided as partisan. In his letter, Cipollone repeatedly derided what he called Democrats' "fundamentally unfair" process.

"Inviting the Administration now to participate in an after-the-fact constitutional law seminar -- with yet-to-be-named witnesses -- only demonstrates further the countless procedural deficiencies that have infected this inquiry from its inception and shows the lack of seriousness with which you are undertaking these proceedings," Cipollone wrote.

Nadler had written the president last week announcing a hearing for Dec. 4 at 10 a.m., and notified him of the committee’s intentions to provide him with “certain privileges” while they consider "whether to recommend articles of impeachment to the full House.” Nadler also extended an invitation to the president, asking whether “you and your counsel plan to attend the hearing or make a request to question the witness panel.”

With polls showing support for impeachment flagging, Democrats were aiming for a final House vote by Christmas, which would set the stage for a likely Senate trial in January. Surveys have shown that independents are souring on the idea of impeaching and removing Trump from office, including in critical battleground states like Wisconsin, even as House Democrats aggressively presented their focus-group-tested "bribery" case against the president over the past two weeks.

“I do believe that all evidence certainly will be included in that report so the Judiciary Committee can make the necessary decisions that they need to,” said Rep. Val Demings, D-Fla., a member of both the Intelligence and Judiciary committees.

She said Democrats had not yet finalized witnesses for the upcoming Judiciary hearings and were waiting to hear back from Trump on his plans to present a defense.

“If he has not done anything wrong, we’re certainly anxious to hear his explanation of that,” Demings said.

The House Judiciary's impeachment hearings will follow last month's hearings by the House Intelligence Committee, which heard from 12 witnesses during five days of testimony.

Trump has previously suggested that he might be willing to offer written testimony under certain conditions, though aides suggested they did not anticipate Democrats would ever agree to them.

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“The Democrats are holding the most ridiculous Impeachment hearings in history. Read the Transcripts, NOTHING was done or said wrong!” Trump tweeted Saturday.

Late Sunday, Trump tweeted a link to a Fox News opinion piece written by legal analyst Gregg Jarrett, and quoted the piece as saying the president had done "nothing impeachable."

Fox News' Brooke Singman and The Associated Press contributed to this report.