A federal judge on Monday ordered former White House counsel Donald McGahn to appear before Congress in a setback to President Donald Trump's effort to keep his top aides from testifying.

The outcome could lead to renewed efforts by House Democrats to compel testimony from other high-ranking officials, including former national security adviser John Bolton.

Not even the president's closest aides who receive a subpoena from Congress can "ignore or defy congressional compulsory process, by order of the President or otherwise," Judge Ketanji Brown Jackson wrote in ruling on a lawsuit filed by the House Judiciary Committee.

McGahn was a star witness in special counsel Robert Mueller's investigation, and Democrats wanted to question McGahn about possible obstruction of justice by Trump. That was months before the House started an impeachment inquiry into Trump's effort to get Ukraine to announce an investigation of former Vice President Joe Biden.

The administration will appeal Jackson's ruling. "This decision contradicts longstanding legal precedent established by Administrations of both political parties," White House press secretary Stephanie Grisham said. "We will appeal and are confident that the important constitutional principle advanced by the Administration will be vindicated."

The Justice Department will seek to put the ruling on hold in the meantime, department spokeswoman Kerri Kupec said.

William Burck, an attorney for McGahn, said the former White House counsel will comply with the subpoena, absent a court-imposed stay.

Rep. Jerrold Nadler, D-N.Y., the Judiciary Committee chairman, said he hoped McGahn would "promptly appear before the committee."

The White House has argued that McGahn and other witnesses have "absolute immunity" from testifying.

But such immunity " simply does not exist," Jackson wrote in a 118-page ruling. "That is to say, however busy or essential a presidential aide might be, and whatever their proximity to sensitive domestic and national-security projects, the President does not have the power to excuse him or her" from complying with a valid congressional subpoena, Jackson wrote. She is an appointee of President Barack Obama.

Whether McGahn has to provide all the information Congress seeks, though, is another matter, the judge wrote. The president may be able to assert "executive privilege" on some sensitive issues, she wrote.

McGahn was a vital witness for Mueller, whose April report detailed the president's outrage over the investigation into Russian meddling in the 2016 election and Trump's efforts to curtail it.

In interviews with Mueller's team, McGahn described being called at home by the president on the night of June 17, 2017, and being directed to call the Justice Department and say Mueller had conflicts of interest and should be removed. McGahn declined the command, deciding he would resign rather than carry it out, the report said.

Once that episode became public in the news media, the report said, the president demanded that McGahn dispute the news stories and asked him why he had told Mueller about it and why he had taken notes of their conversations. McGahn refused to back down.

It's unclear if McGahn's testimony would include any new revelations beyond what Mueller has already released. Mueller concluded that he could not exonerate Trump on obstruction of justice, but also that there was insufficient evidence to prove a criminal conspiracy between Trump's campaign and Russia.

House Democrats leading the impeachment inquiry have yet to try to force Bolton to testify, and a subpoena for Bolton's former deputy, Charles Kupperman, to appear was withdrawn. Democrats have said they don't want to get bogged down in court fights over testimony.

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Associated Press writer Eric Tucker contributed to this report.