FILE PHOTO: White House Counsel Don McGahn sits behind U.S. President Donald Trump as the president holds a cabinet meeting at the White House in Washington, U.S. June 21, 2018. REUTERS/Jonathan Ernst/File Photo Reuters

The former White House counsel Don McGahn has been ordered by a federal judge to testify before a congressional committee.

McGahn was a key witness in the special counsel Robert Mueller’s Russia investigation and spent 30 hours testifying before Mueller’s team.

He was subpoenaed in April by the House Judiciary Committee to testify again.

McGahn’s attorney said his client would comply with the decision unless an appeal were filed; administration officials said they intended to appeal.

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A federal judge ruled on Monday that the former White House counsel Don McGahn must appear before a congressional committee — a setback in President Donald Trump’s efforts to prevent top White House staff members from testifying against him.

McGahn was a key witness in the special counsel Robert Mueller’s Russia investigation, particularly the part focused on whether Trump obstructed justice. McGahn spent 30 hours testifying before Mueller’s team and was featured heavily in Mueller’s findings. He was subpoenaed in April by the House Judiciary Committee.

Mueller did not make a determination on obstruction of justice, saying that the report „did not exonerate“ Trump but that charging the president with a crime was „not an option we could consider“ given Justice Department policy regarding sitting presidents.

Judge Ketanji Brown Jackson made her ruling on Monday and said McGahn must comply with the House subpoena to testify.

„Stated simply, the primary takeaway from the past 250 years of recorded American history is that presidents are not kings,“ Jackson said in her ruling. „This means that they do not have subjects, bound by loyalty or blood, whose destiny they are entitled to control.“

She continued: „Rather, in this land of liberty, it is indisputable that current and former employees of the White House work for the people of the United States, and that they take an oath to protect and defend the Constitution of the United States. Moreover, as citizens of the United States, current and former senior-level presidential aides have constitutional rights, including the right to free speech, and they retain these rights even after they have transitioned back into private life.“

The White House has argued that McGahn and other top aides have „absolute immunity“ from testifying.

But Jackson said in her ruling that the president „does not have the power to excuse him or her“ from complying with a congressional subpoena: „Fifty years of say so within the executive branch does not change that fundamental truth.“

„Accordingly,“ Jackson added, „just as with Harriet Miers before him, Donald McGahn ‚must appear before the Committee to provide testimony, and invoke executive privilege where appropriate.'“

William Burck, McGahn’s attorney, said his client would comply with the decision unless an appeal were filed.

„Don McGahn will comply with Judge Jackson’s decision unless it is stayed pending appeal,“ Burck said, adding that the Department of Justice was handling this case, „so you will need to ask them whether they intend to seek a stay.“

A DOJ spokeswoman, Kerri Kupec, told Bloomberg News‘ Jordan Fabian that the agency would appeal the ruling.

„This decision contradicts long-standing legal precedent established by administrations of both political parties,“ the White House press secretary, Stephanie Grisham, said in a statement to CNN. „We will appeal and are confident that the important constitutional principle advanced by the administration will be vindicated.“

The House Judiciary Committee’s chairman, Jerry Nadler, said he hoped the ruling would encourage McGahn to „promptly appear before the committee.“

Reuters cited legal experts as saying the ruling could encourage other administration officials to come forward and testify in House Democrats‘ impeachment inquiry, which the White House has ordered top aides not to cooperate with.

The impeachment investigation is centered on a July 25 phone call between Trump and Ukrainian President Volodymyr Zelensky and looks at whether Trump abused his power in trying to get Ukraine to announce investigations that would benefit Trump politically.

Read the full ruling here: