Pelosi says the step is being taken to ‘to eliminate any doubt’ over the legitimacy of the Trump impeachment inquiry.

Democrats in the United States House of Representatives set a Thursday vote to lay out next steps for their impeachment inquiry of President Donald Trump, even as officials past and present refuse to cooperate.

Trump and his fellow Republicans have spent weeks branding the probe illegitimate because the full Democratic-led House had not authorised it. If the measure passes the House, Democrats are likely to argue that it neutralises those claims.

Speaker of the House Nancy Pelosi, in a letter to fellow Democrats, said the step is being taken “to eliminate any doubt” about the process as the White House continues its attempt to block witnesses and withhold documents.

Several administration officials, including a former deputy national security adviser on Monday, have failed to testify to House committees engaged in the impeachment probe.

Charles Kupperman, a deputy to former national security adviser John Bolton, defied a House subpoena on Monday to testify as part of the investigation, escalating the standoff between the White House, who has categorically said it will not comply with the inquiry, and Congress.

Kupperman filed a lawsuit in federal court in Washington, DC, asking for a ruling on whether he was legally required to appear. In a statement, Kupperman said he was awaiting “judicial clarity” on the matter.

In a letter in early October, White House counsel Pat Cipollone said the administration would not cooperate with the inquiry, which he argued denied the president due process. He also said that the impeachment inquiry was not official without a House voting on it, a claim that legal experts say is incorrect, as the Constitution requires no such vote to begin impeachment.

The impeachment probe seeks to answer whether Trump withheld nearly $400m in military aid from Ukraine in an attempt to pressure officials into investigating a gas company linked to the son of 2020 Democratic presidential hopeful Joe Biden.

Trump has denied any wrongdoing.

Republicans have in recent days accused Democrats of not being transparent in the investigation, also citing the lack of a vote to say the impeachment inquiry is illegitimate.

In the letter to colleagues, Pelosi said the resolution will “affirm the ongoing, existing investigation” and lay out procedures for open hearings and the next steps going forward.

Despite the announcement, Pelosi reiterated that the impeachment inquiry does not require the vote.

“Of course, this argument has no merit,” she said.

‘Lengthy game of rope-a-dope’

Kupperman’s lawsuit argues that he is stuck between the “competing demands of both the legislative and executive branches”.

Without the court’s help, he said he would have to make the decision on which branch of government to obey, which could “inflict grave constitutional injury” on either Congress or the presidency.

“Given the issue of separation of powers in this matter, it would be reasonable and appropriate to expect that all parties would want judicial clarity,” Kupperman said in a statement.

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Meanwhile, House Intelligence Chairman Adam Schiff said Kupperman’s suit has “no basis in law”. He also speculated that the White House did not want Kupperman to testify because his testimony could be incriminating.

“If this witness had something to say that would be helpful to the White House, they would’ve wanted him to come and testify,” Schiff told reporters. “They plainly don’t.”

Schiff said the three committees leading the impeachment inquiry will move ahead with the investigation, with or without testimony from Kupperman and other witnesses. Democrats have indicated that they are likely to use the president’s letter and the no-show witnesses to write an article of impeachment against Trump for obstruction of justice, rather than individually challenge the noncompliance in court.

“We are not willing to allow the White House to engage us in a lengthy game of rope-a-dope in the courts, so we will move forward,” Schiff said.

Two current National Security Council staff members, Alexander Vindman and Tim Morrison, are scheduled to testify before the House later this week and would be the first White House employees to testify in the inquiry. Morrison’s lawyer, Barbara Van Gelder, said in an email to the Associated Press on Monday that if Morrison is subpoenaed, he will appear.

Pivot to White House

After hearing from a series of State Department officials, the three House committees leading the impeachment investigation are turning their focus to the White House. Democrats say they are hoping to get more answers about what aides close to Trump knew about his orders on Ukraine policy.

Several State Department officials have already testified that they were concerned about Trump’s personal lawyer Rudy Giuliani’s unofficial role in Ukraine foreign policy, and his apparent campaign to push out the US ambassador to Ukraine, Marie Yovanovitch.

In a significant development last week, William Taylor, the current top diplomat in Ukraine, testified that he was told that aid to Ukraine would be withheld until the country conducted investigations into US politics.