A Washington federal judge has been asked to declare whether a former Trump administration national security official can lawfully testify as part of the House impeachment inquiry, despite an assertion from the White House that the adviser is entitled to immunity and cannot be forced to sit for a deposition.

The former official, Charles Kupperman, represented by Charles Cooper of the Washington boutique firm Cooper & Kirk, named President Donald Trump and House Democrats as defendants in the complaint in U.S. District Court for the District of Columbia. Kupperman had been scheduled to testify Monday morning, but he did not show up.

U.S. District Judge Richard Leon was assigned Monday afternoon to preside over the dispute, the first that directly confronts testimony from a would-be witness in the House's impeachment inquiry. The inquiry, focused on whether Trump abused the power of the presidency by asking Ukraine to investigate a chief political rival of Trump, has secured testimony from nine other witnesses.

Leading House Democrats reportedly called Kupperman's lawsuit "an obvious and desperate tactic by the president to delay and obstruct the lawful constitutional functions of Congress and conceal evidence about his conduct from the impeachment inquiry." House leaders said Monday they will "move forward" with the inquiry despite the lawsuit.

"The lawsuit that Dr. Kupperman filed has no basis in law. A private citizen cannot sue the Congress to try to avoid coming in when they are served with a lawful subpoena," U.S. Rep. Adam Schiff, chair of the House Intelligence Committee, said Monday. "We expect that the court will make short shrift of that argument."

Any failures to appear by witnesses, Schiff said, will build a "powerful case" for an obstruction case against Trump. "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 said Monday.

The Trump White House tried several weeks ago to thwart any cooperation from the administration with House Democrats. The White House has derided the impeachment inquiry as "constitutionally defective," a position ridiculed by conservative and progressive lawyers. The Trump White House has largely failed to stop officials from speaking with House Democrats.

Witnesses appearing before House investigators have confronted Trump's plan to withhold $391 million in security aid to Ukraine until leaders there agreed to investigate Democratic presidential contender Joe Biden and his son Hunter. One top U.S. diplomat, Gordon Sondland, represented by Paul Hastings partner Robert Luskin, said the pressure Trump put on Ukraine amounted to a quid pro quo, according to a report from The Wall Street Journal. Trump has denied any illegal effort to enlist a foreign power to influence U.S. elections, claiming that his July 25 call with the president of Ukraine was "perfect."

Kupperman, a former deputy national security adviser, "is faced with irreconcilable commands by the legislative and executive branches of the government," Cooper wrote in the lawsuit. Cooper said his client "obviously cannot satisfy the competing demands of both the legislative and executive branches, and he is aware of no controlling judicial authority definitively establishing which branch's command should prevail."

Cooper said Kupperman "takes no position on whether the command of the legislative branch or the command of the executive branch should prevail; he seeks only to carry out whichever constitutional obligation the Judicial Branch determines to be lawful and binding."

Trump-appointed leaders at the Justice Department have broadly argued that current and former administration officials are immune from congressional demands for information.

Those assertions are being contested in various court cases, including one that demands testimony from Donald McGahn, the former White House counsel who has since returned to the law firm Jones Day. McGahn was a central witness in the special counsel's investigation of the Trump campaign's ties to Russia and the president's purported efforts to derail the investigation through allegedly obstructive acts.

Pat Cipollone, the White House counsel, said in a letter to Cooper that Kupperman was not permitted to testify in the impeachment inquiry. Cooper had asked the White House for its position on the subpoena the House issued to Kupperman.

"[I]n order to protect the prerogatives of the office of president today and in the future, and in response to your request, the president directs Mr. Kupperman not to appear at the committee's scheduled hearing on Monday, October 28, 2019," Cipollone wrote. "This long-standing principle is firmly rooted in the Constitution's separation of powers and protects the core functions of the presidency."

The policy Cipollone pointed to "applies only to senior White House advisers," according to a post at Just Security from former congressional lawyer Michael Stern. "There is nothing in Cipollone's October 25 letter to suggest that Kupperman is prohibited from testifying because the House inquiry is invalid or on any other ground that would be broadly applicable to administration officials," Stern wrote.

Charles Cooper Charles Cooper, of Cooper & Kirk at the White House last year. (Photo: Diegp M. Radzinschi/ALM)

Cooper is a well-known Republican lawyer who ran the Justice Department's office of legal counsel in the George H.W. Bush administration. He represented Jeff Sessions, then the U.S. attorney general, in the special counsel's Russia investigation. Cooper also now represents John Bolton, the former Trump national security adviser who resigned last month.

Bolton is widely seen as a critical witness for House investigators as part of the impeachment inquiry.

University of California Berkeley School of Law professor John Yoo, a former George W. Bush administration Justice Department leader, told The New York Times that the Trump White House would likely "go to the mat" to block any deposition of Bolton, who played a central role in U.S. foreign policy initiatives.

"If the White House were to fight the House impeachment on executive privilege grounds, Bolton would be the hill on which to die," Yoo told the Times. "The Trump White House could claim not just that the impeachment investigation is illegitimate, which is its current line of defense, but that it is defending the right of future presidents to have an effective White House and to conduct a successful foreign policy."

Cooper's complaint is posted below: