House Democrats are now demanding the testimony of a damning Mueller witness

House Judiciary Chair Jerry Nadler sent a subpoena Monday to former White House Counsel Don McGahn, one of the key witnesses in Special Counsel Robert Mueller's report.

McGahn, the report makes clear, gave extensive testimony to Mueller about his time working in the White House. Since he was an administration lawyer and not President Donald Trump's personal legal counsel, his interactions with Trump are not covered by attorney-client privilege.

The subpoena is particularly important because McGahn's accounts in the report include some of the most damning material for the president. McGahn recounted how Trump repeatedly tried to get him to fire Mueller as the Russia investigation was ongoing in the summer of 2017. These demands made McGahn so uncomfortable, according to the report, that he nearly resigned in protest. Instead, he waited the president out, and Trump apparently backed off from the request. However, as the report shows, Trump went on to engage in more efforts that could obstruct justice.

Later, when media reports broke about Trump's demand that McGahn fire Mueller, the president reportedly tried to get McGahn to create a false record that would contradict the true claim he had been so ordered, the report said.

Mueller demonstrates how these acts could be shown to conform to the key elements of an obstruction of justice charge.

The hearing, according to the subpoena, is scheduled for May 21. McGahn is also told to deliver documents on 36 topics to the committee by May 7.

Nadler has confirmed that he believes the conduct Mueller uncovered and described could be worthy of impeachment.

"I do think, if proven, which hasn't been proven yet, if proven, some of this would be impeachable, yes," he said Sunday. "Obstruction of justice, if proven, would be impeachable."

But Georgia Republican Rep. Doug Collins, the ranking member of the committee, denounced Nadler's move to issue a subpoena.

"Don McGahn sat for more than 30 hours of interviews with the special counsel's investigation, and the chairman has answered that with a stunning 36-item subpoena," said Collins. "Instead of looking at material that Attorney General Barr has already made available, Democrats prefer to demand additional materials they know are subject to constitutional and common-law privileges and cannot be produced."