Washington: House Democrats moved quickly on Monday to bring their impeachment case against United States President Donald 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 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 Trump. It will be the first time all House lawmakers will be asked to go on record regarding 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-authorised subpoenas or continue obstructing the House of Representatives,” 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 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,” 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 authorise 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 authorisation for the inquiry, a step that is not required by the Constitution or House rules. In scheduling a vote now, Democrats were effectively challenging Trump and his congressional allies who have called 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 legitimise the Schiff/Pelosi sham impeachment,” Representative Kevin McCarthy (Republican, from Calfornia), the House minority leader, said in a tweet.

Stephanie Grisham, the White House press secretary, said Pelosi was “finally admitting what the rest of America already knew — that Democrats were conducting an unauthorised 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. Pelosi reiterated what Democrats have argued for weeks and a US 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 Joe Biden 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 Schiff. The White House had said last Friday that 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 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,” Schiff said. “They plainly don’t.”

Schiff conceded that the White House would most likely try to invoke similar privilege to try to block other crucial witnesses, including John Bolton, the former national security adviser said to be alarmed by Trump’s dealings with Ukraine. Doing so would only fuel another article of impeachment charging Trump with obstructing Congress’ fact-finding, he said.