House Democrats announced they will subpoena White House documents relevant to their impeachment inquiry, a move likely to bring impeachment into federal courtrooms.

Supported by House Speaker Nancy Pelosi, the three lead committee chairman—Maryland’s Elijah Cummings of the oversight committee, California’s Adam Schiff of the intelligence committee, and New York’s Eliot Engel of foreign affairs—sent a letter to the White House on Wednesday demanding material establishing, among other things, who in the administration knew about the fateful July 25 phone call between President Donald Trump and Ukrainian President Volodomyr Zelensky, as well as the run-up to it.

On that phone call, Trump pressed Zelensky to investigate political rival Joe Biden as a “favor” after Zelensky expressed interest in purchasing additional anti-tank missiles from the United States.

Their previous attempts at voluntary White House compliance rebuffed, the Democrats are demanding documents establishing “the identity of all individuals” within the government knowledgeable about that call and a previous call with Zelensky on April 21. They also want records of discussions those individuals had concerning the substance of the calls.

A bevy of current and former National Security Council officials, including fired national security adviser John Bolton, are referenced in the subpoena request, as is Energy Secretary Rick Perry, the senior U.S. official attending Zelensky’s inauguration. Prominently featured as well are Attorney General Bill Barr, Secretary of State Mike Pompeo, and their subordinates. Pompeo, who on Tuesday signaled defiance of a previous House subpoena for testimony from State officials, admitted in Rome on Wednesday that he was on the July 25 call with Zelensky.

The latest subpoena request came hours before another headache for Pompeo. The State Department’s inspector general will brief House leaders about an ostensibly urgent matter seemingly related to Ukraine. Following that, on Thursday, the Ukraine special envoy Pompeo fired, Kurt Volker, does the same. Next week, so will cashiered U.S. Ambassador Marie Yovanovitch.

While House Democratic leaders have sought to narrow their impeachment focus to the Trump-Zelensky exchange, the new subpoena request opened the aperture somewhat. It seeks documentation of communications between Trump “and the leader of any other foreign country” relevant to “pursuing investigations of President Trump’s political rivals and Ukrainian foreign aid.” That move came after reports that Trump sought to enlist his new U.K. counterpart, Boris Johnson, in discrediting Robert Mueller’s investigation into Russian election interference in 2016. Trump reportedly did the same with Australian PM Scott Morrison.

They’re also seeking records of any effort by Trump or subordinates to “identify or retaliate against” the anonymous whistleblower who, having learned of Trump pressuring Zelensky into the Biden inquiry, reported it to the intelligence-community inspector general. Trump has demanded the release of the whistleblower’s identity, a violation of federal whistleblower protection laws, and publicly suggested violence against the whistleblower’s sources.

Presidencies typically consider internal White House communications to be privileged documents outside the reach of Congress. Schiff, at a Wednesday press conference with Pelosi, reiterated a Democratic position that noncompliance will “be considered evidence of obstruction.” While the Democratic leadership wants the impeachment inquiry to move quickly, Schiff signaled the party’s willingness “to litigate” if necessary to compel disclosure.

Pelosi, who resisted impeachment hearings until news of the Zelensky call emerged, used solemn tones to describe the impeachment proceedings. She pledged they would be fair, dignified, and provide Trump with opportunities to make his case.