The three House committees leading the inquiry are still set to hear from two key witnesses this week. On Tuesday, William Taylor, the top American diplomat in Ukraine, is expected to testify; and on Wednesday, Laura Cooper, who oversees Ukraine- and Russia-related issues at the Pentagon, is slated to appear.

Taylor has emerged as a central figure in the impeachment inquiry, which is examining whether President Donald Trump abused his office by asking Ukraine’s leaders to investigate his political opponents, and whether those probes were tied to military aid to Ukraine that was appropriated by Congress.

In a series of text messages provided to impeachment investigators, Taylor wrote: “I think it’s crazy to withhold security assistance for help with a political campaign.”

Cooper, a career government official, is likely to have knowledge about the decision to withhold military aid to Ukraine — funding viewed as critical for defending itself against Russian aggression to its east.

Philip Reeker, the acting assistant secretary of state for European and Eurasian affairs, was also scheduled to testify on Wednesday, but a source close to him told POLITICO that his deposition was delayed at the committees’ request, citing memorial services for Cummings.

In addition to Reeker, three other officials’ depositions were put on hold: Lt. Col. Alexander Vindman, the director for European affairs at the National Security Council; Suriya Jayanti, a foreign service officer at the U.S. embassy in Kyiv; and Tim Morrison, the Russia chief on the National Security Council.

Meanwhile, some Trump administration officials are still refusing to cooperate.

Trump’s acting budget chief said earlier Monday that he would not testify, citing what he called a “sham process.” His declaration follows that of other executive branch departments and agencies, which have similarly decried the impeachment inquiry as illegitimate.

Russ Vought, the acting director of the Office of Management and Budget, also wrote on Twitter that Michael Duffey — the OMB political appointee tasked with managing a freeze on $400 million in foreign assistance to Ukraine last summer — would not appear for his deposition, either.

Vought joins other Trump administration officials who are stonewalling requests from House Democrats as part of an inquiry into whether the president used the aid as leverage over Ukraine for political favors.

Vought also rejected a House subpoena last week for details about the administration’s decision to withhold the assistance, including a detailed timeline.

But despite the White House’s efforts to block compliance with subpoenas and other requests related to the impeachment inquiry, several current and former officials have appeared for depositions in defiance of the administration — many of whom have offered evidence that Democrats say is critical for their investigation.

