"Given McGahn's central role as a witness to the president's wide-ranging potentially obstructive conduct, the Judiciary Committee can not fulfill its constitutional investigative, oversight and legislative responsibilities - including its consideration of whether to recommend articles of impeachment - without hearing from him", the lawsuit says.
McGahn defied a committee subpoena to testify in May, after the White House directed him not to cooperate with the panel.
The "absolute immunity" doctrine has no grounding in the Constitution, any statutes, or case law and never has been accepted by any court, Democrats argued in the lawsuit, which filed by House General Counsel Douglas Letter.
Last month, the Judiciary panel filed suit asking a federal court to force the release of grand jury information from Mueller's investigation.
The outcome of the court fight that Democrats started on Wednesday could set the precedent for a litany of House subpoenas attempting to obtain documents or compel testimony from various officials in the Trump administration, as well as for future fights over executive privilege between the executive and legislative branches.
"The Judiciary Committee is now determining whether to recommend articles of impeachment", the lawsuit said. The measure passed 229-191 on a pure party-line vote.
House Oversight Chairman Elijah Cummings of Maryland said at the National Press Club on Wednesday that he backs Pelosi's position "that the time for impeachment may come".
In a May 20 letter to House Judiciary Chairman Jerrold Nadler, current White House counsel Pat Cipollone wrote that an internal Justice Department opinion determined Congress can not compel the president's senior advisers to testify about their official duties.
"Chairman Nadler will file a complaint in court today to enforce a subpoena to compel former White House Counsel Don McGahn to testify before the committee", Pelosi said in a letter to Democrats in the House of Representatives that focused mainly on combating gun violence. Every single Democrat on the Senate Judiciary Committee, with the exception of Sen.
House Democrats are sharply divided on the question of impeachment, with just over half, including Nadler, favoring proceedings.
"No one is above the law", House Speaker Nancy Pelosi said, citing the planned litigation in a memo to Democratic colleagues. The subpoena to McGahn is one of a number the committee has issued and been rebuffed by the White House: both former communications director Hope Hicks and former McGahn deputy Annie Donaldson did not answer almost all of the questions that the committee asked of them related to their time at the White House.
The House members requested production on a rolling basis - starting with the White House Counsel Office materials covered under Grassley's original request - and said that they would work with the archive agency to streamline the process for the staff secretary document production.