In the ever-escalating skirmish between U.S. House Democrats and the Trump administration, there’s now a new defendant: Donald McGahn, the former White House counsel and key witness in the special counsel’s investigation of Russia’s interference in the 2016 election.

House Democrats on Wednesday sued McGahn in Washington’s federal trial court to force him to comply with a subpoena seeking testimony about his time leading the White House counsel’s office and interaction with President Trump.

“The Judiciary Committee is now determining whether to recommend articles of impeachment against the president based on the obstructive conduct described by the special counsel. But it cannot fulfill this most solemn constitutional responsibility without hearing testimony from a crucial witness to these events: former White House Counsel Donald F. McGahn II,” House general counsel Douglas Letter said in the complaint. “McGahn, however, has defied a Congressional subpoena to appear before the Judiciary Committee, at the direction of President Trump, who claims McGahn is “absolutely immune” from testifying, a claim with no basis in law.”

Annie Owens and Joshua Geltzer of the Institute for Constitutional Advocacy and Protection at Georgetown University Law Center appeared on the complaint with a team of lawyers from the House’s general counsel’s office.

The lawsuit, which was assigned to Chief Judge Beryl Howell, will test the scope of the Trump administration’s oft-used assertions of executive privilege to stymie the release of information tied to the Russia probe. McGahn’s lawyer, William Burck of Quinn Emanuel Urquhart & Sullivan, said in May that McGahn was refusing to appear to testify at the wishes of the White House.

The White House had instructed McGahn, who’s now back at Jones Day as a partner in Washington, to defy a subpoena from the House Judiciary Committee. The committee is demanding McGahn testify about former special counsel Robert Mueller III’s investigation into Russian interference in the presidential elections. McGahn was a key witness, one who interacted daily with the president and who reportedly rebuffed his efforts to interfere in the investigation.

The lawsuit confronts Trump’s efforts to stop McGahn from appearing before the House, and includes public statements from the president saying, “We’re fighting all the subpoenas,” and “I don’t want people testifying.”

“Consistent with that approach, the president has sought to prevent McGahn—now a private citizen—from testifying before the Judiciary Committee,” the lawsuit said. “The day before McGahn’s required appearance before the Judiciary Committee pursuant to the subpoena at issue in this litigation, the president purported to direct McGahn not to appear, claiming that McGahn is ‘absolutely immune’ from compelled testimony. The next day, without offering any accommodation, McGahn failed to appear based on the president’s directive.”

Robert Mueller Robert Mueller III, former special counsel for the U.S. Department of Justice, testifies before the House Judiciary Committee in Washington, D.C., on  July 24, 2019.

The Justice Department’s Office of Legal Counsel argued in a 15-page legal opinion, published this year, that the president could stop McGahn from testifying. The opinion pointed to a 1999 opinion that said a congressional subpoena requiring a senior presidential adviser to testify would be “akin to” requiring the president himself to appear.

Mueller testified for more than five hours on Wednesday about his 448-page report showing Russia’s efforts to meddle in the 2016 election and incidents in which Trump allegedly tried to derail the special counsel’s investigation. Trump has denied any move to obstruct the investigation.

McGahn cooperated extensively with Mueller’s team, speaking for more than 30 hours about his interactions with Trump. The report showed among other things that Trump pushed McGahn to find a way to fire Mueller based on the president’s contention that the special counsel had conflicts of interests. Mueller told House lawmakers on Wednesday he had no such conflict.

McGahn said he refused to engage with then-Deputy Attorney General Rod Rosenstein over firing Mueller, saying that any move might make it seem the president was trying to “meddle in the investigation.”

The lawsuit against McGahn comes as House Democrats are waging a series of court fights that seek financial records and other information Trump has long sought to shield from the public. Trump told voters in 2016 he would release his tax returns, as presidents in modern times have done, but the president has since refused any disclosure.

The House last month sued the Treasury Department and the IRS for copies of Trump’s tax returns, and Trump has sued the House Ways and Means Committee from requesting or obtaining copies of his state tax returns from New York agencies. This week, Trump filed suit in California court to stop a new state law that requires presidential candidates to release their tax returns in order to appear on the ballot.

Meanwhile, two federal judges have upheld congressional committee subpoenas that command Trump’s accounting firm and his longtime lender, Deutsche Bank, to turn over financial records. A federal appeals panel recently appeared inclined to rule against Trump in the case involving his accountant Mazars USA, and the Deutsche Bank case will be heard next month in New York.

Several other lawsuits contend that Trump’s continued profiting from his business ventures while in office is violating the constitutional check against presidents receiving foreign and domestic “emoluments.” One appeals court ruled in his favor, dismissing a suit, while another case, brought by congressional Democrats, is pending in Washington’s federal trial court.

The House suit against McGahn is posted below: