WASHINGTON — House Democrats moved quickly on Monday to bring their impeachment case against President Trump into the open, saying they would forgo court battles with defiant witnesses and would vote this week on procedures to govern nationally televised hearings.
Representative Adam B. Schiff, the House Intelligence Committee chairman who is leading the inquiry, said that Democrats would not wait to fight the Trump administration in court as it moves to block key witness testimony. Instead, after Mr. Trump’s former deputy national security adviser defied a subpoena, he issued a warning: White House directives not to cooperate would only bolster the case that the president had abused his office and obstructed Congress.
By the afternoon, Speaker Nancy Pelosi added to that sense of urgency, announcing that after weeks of private fact-finding, the full House would vote on Thursday to initiate a public phase of the inquiry. That vote would establish rules for the public presentation of evidence and outline due process rights for Mr. Trump.
It will be the first time all House lawmakers will be asked to go on record on the investigation since it began in September, something Democrats had so far resisted.
“We are taking this step to eliminate any doubt as to whether the Trump administration may withhold documents, prevent witness testimony, disregard duly authorized subpoenas or continue obstructing the House of Representatives,” Ms. Pelosi said in a letter to colleagues. “Nobody is above the law.”
The announcements sent the clearest signals to date that Democrats believe their month-old inquiry is on track and will allow them to begin making an effective impeachment case before the nation by Thanksgiving. Party leaders are wary that their investigation, which focuses on Mr. Trump’s attempts to pressure a foreign nation to investigate his political rivals, will lose momentum and drag on into next year without a vote on articles of impeachment.
In earlier oversight disputes, House Democrats have turned to the courts with some frequency. But those lawsuits have eaten up valuable months without signs of resolution any time soon — time that impeachment investigators do not have.
“We are not willing to let the White House engage us in a lengthy game of rope-a-dope in the courts, so we press ahead,” Mr. Schiff told reporters outside his secure hearing rooms.
Democrats have resisted for weeks the idea of holding a vote on the impeachment inquiry, arguing that doing so was unnecessary to authorize their work, and privately worrying that a floor vote could put politically vulnerable Democrats in a difficult position.
But they have come under intense criticism from Republicans for failing to seek formal authorization for the inquiry, a step that is not required by the Constitution or House rules. In scheduling a vote now, Democrats were effectively challenging Mr. Trump and his congressional allies, who have called the inquiry the inquiry unfair and the process a sham, but avoided any substantive discussion of the president’s conduct.
Still, Republicans signaled that after weeks of calling for a vote on the inquiry, they would oppose the resolution en masse.
“We will not legitimize the Schiff/Pelosi sham impeachment,” Representative Kevin McCarthy, Republican of California and the minority leader, said in a tweet.
Stephanie Grisham, the White House press secretary, said Ms. Pelosi was “finally admitting what the rest of America already knew — that Democrats were conducting an unauthorized impeachment proceeding, refusing to give the president due process, and their secret, shady, closed door depositions are completely and irreversibly illegitimate.”
Democrats said their inquiry has been proper from the start. Ms. Pelosi reiterated what Democrats have argued for weeks and a Federal District Court judge ruled last week: that they did not need a formal vote of the full House to start a legitimate inquiry. (The Justice Department separately announced Monday it would appeal the ruling handed down Friday.)
So far, the work of the impeachment inquiry has mostly been done out of public view, with staff for Democrats and Republicans questioning a growing roster of diplomats and other administration officials in the closed chambers of the House Intelligence Committee. Democrats are pleased with the portrait they have assembled of a president who bypassed the normal channels of diplomacy to pressure Ukraine to investigate former Vice President Joseph R. Biden Jr. and unproven theories that could exonerate Russia from aiding his campaign in 2016 and implicate Democrats in interfering in the election instead.
That work was briefly interrupted on Monday, when Charles M. Kupperman, the former deputy national security adviser, defied a House subpoena for testimony, angering Mr. Schiff. The White House said on Friday that Mr. Kupperman, as one of the president’s “closest confidential” advisers, was immune from testifying, and directed him not to appear in defiance of a subpoena. That prompted him to file a lawsuit against Mr. Trump and congressional Democrats asking a federal judge whether he could testify, raising the prospect of a drawn-out legal battle over weighty questions about the separation of powers that could effectively stall the impeachment inquiry for months.
“If this witness had something to say that would be helpful to the White House, they would want him to come and testify,” Mr. Schiff said of Mr. Kupperman. “They plainly don’t.”
Mr. Schiff conceded that the White House would most likely try to invoke similar privilege to try to block other crucial witnesses, including John R. Bolton, the former national security adviser, who is said to be alarmed by Mr. Trump’s dealings with Ukraine. Doing so would only fuel another article of impeachment charging Mr. Trump with obstructing Congress’s fact-finding, he said.
As many as five more officials are expected to testify in closed session this week, including Lt. Col. Alexander S. Vindman, the top Ukraine expert on the National Security Council, who is scheduled to appear on Tuesday. He plans to detail his concerns about Mr. Trump’s attempts to pressure Ukraine to investigate his political rivals.
But if Democrats are going to convince the public — and potentially some Republicans — that Mr. Trump’s behavior warrants making him only the third president in American history to be impeached, they know they will have to secure clear and damning testimony out in the open.
Democrats described the vote as a necessary step.
“This resolution establishes the procedure for hearings that are open to the American people, authorizes the disclosure of deposition transcripts, outlines procedures to transfer evidence to the Judiciary Committee as it considers potential articles of impeachment, and sets forth due process rights for the president and his counsel,” Ms. Pelosi said in her letter.
Though aides for several committees were still drafting the resolution Monday evening, the rough outlines of the next phase of the inquiry began to come into view.
After it wraps up its closed witness depositions in the coming weeks, the House Intelligence Committee will begin to hold public hearings with key witnesses, such as Gordon D. Sondland, the American ambassador to the European Union; Fiona Hill, a former top White House adviser; and William B. Taylor Jr., the top American diplomat in Ukraine.
The rules will allow for the committee’s staff aides to question witnesses directly during public hearings, according to an official working on the inquiry who described the measure on condition of anonymity because it had yet to be made public.
When the panel concludes its fact-finding, Mr. Schiff will transmit raw evidence and, potentially, a written report on his findings to the House Judiciary Committee, the venue where presidential impeachment articles have traditionally been drafted and debated. In that sense, Mr. Schiff could play a role roughly akin to Ken Starr, the independent counsel who presented the results of his investigation into President Bill Clinton to the committee in 1998 as it weighed impeachment.
The Judiciary Committee would then be responsible for convening hearings to consider additional evidence, draft articles of impeachment and vote on whether to recommend them to the full House. It is at that stage when Democrats appear poised to give Mr. Trump and his legal team a chance to offer input on the case. It was not clear Monday evening how far they would go in granting them the right to call or cross-examine witnesses, as lawyers for Mr. Clinton and President Richard M. Nixon were allowed to do in earlier proceedings.
Charlie Savage contributed reporting.