Three House committee chairs are readying a subpoena for the White House to demand key documents related to the July 25 phone call between President Trump and the Ukrainian president. This subpoena is part of the impeachment inquiry into whether Mr. Trump jeopardized national security during the call by pressing Ukraine to investigate former Vice President Joe Biden, a political rival.

Chairman Adam Schiff of the Intelligence Committee, Eliot Engel of the Foreign Affairs Committee and Elijah Cummings of the Oversight Committee released a memo and draft subpoena on Wednesday. They previously requested unsuccessfully that the White House produce these documents in letters on September 9 and September 24.

"Over the past several weeks, the Committees tried several times to obtain voluntary compliance with our requests for documents, but the White House has refused to engage with — or even respond to — the Committees," the memo said.

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The subpoena will be issued on Friday, October 4, if the White House does not comply before then.

Meanwhile, on Tuesday, Secretary of State Mike Pompeo accused Democrats of trying to "bully" and "intimidate" State Department officials by scheduling depositions about their involvement with President Trump's call with the Ukrainian president on short notice.

Pompeo confirmed Wednesday that he was on the call between Mr. Trump and the Ukrainian president. That development prompted the chairmen of three committees to warn Pompeo he would be considered a "fact witness" and should play no role in dictating investigators' access to witnesses or documents.

"He should immediately cease intimidating Department witnesses in order to protect himself and the President," they said in a statement.