US District Judge Ketanji Brown Jackson ruled on Monday that former White House Counsel Don McGahn must comply with the House subpoena to testify before Congress.

McGahn was a key witness in former special counsel Robert Mueller's Russia investigation, particularly into the investigation of whether the president obstructed justice. He was subpoenaed in April by the House Judiciary Committee.

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

Jackson's ruling on McGahn would not bind other officials. But some lawyers told Reuters that Bolton and others could use the ruling to justify talking to Congress if they decide doing so would be in their self-interest.

"It could be a warm embrace for those who want to testify but need a reason to do," Jessica Levinson, a law professor at Loyola Law School in Los Angeles, told Reuters. "It would give political cover to those who want to come forward."

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A court ruling on Monday could give cover to former national security advisor John Bolton and other administration officials to cooperate in the impeachment inquiry against President Donald Trump, legal experts said.

US District Judge Ketanji Brown Jackson made her ruling on Monday and said former White House Counsel Don McGahn must comply with the House subpoena to testify before Congress.

McGahn was a key witness in former special counsel Robert Mueller's Russia investigation, particularly into the investigation of whether the president 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.

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

"Don McGahn will comply with Judge Jackson's decision unless it is stayed pending appeal. The [Department of Justice] is handling this case, so you will need to ask them whether they intend to seek a stay."

DOJ spokeswoman Kerri Kupec told Bloomberg News' Jordan Fabian that the DOJ would appeal the ruling.

The Trump administration has argued that the US Constitution does not give congress power to compel testimony from senior members of the executive branch.

Jackson's ruling on McGahn would not bind other officials. But some lawyers told Reuters that Bolton and others could use the ruling to justify talking to Congress if they decide doing so would be in their self-interest.

The ruling may be used as 'political cover to those who want to come forward'

FILE - In this Sept. 4, 2018 file photo, White House counsel Don McGahn, listens as he attends a confirmation hearing for Supreme Court nominee Brett Kavanaugh before the Senate Judiciary Committee on Capitol Hill in Washington. (AP Photo/Jacquelyn Martin) Associated Press

This month, Bolton's lawyer said in a letter that Bolton "stands ready" to testify if a judge ruled that Congress has the authority to make him appear. However, Bolton did not appear for a closed-door deposition on Nov. 7.

"It could be a warm embrace for those who want to testify but need a reason to do," Jessica Levinson, a law professor at Loyola Law School in Los Angeles, told Reuters. "It would give political cover to those who want to come forward."

Bolton's lawyer Charles Cooper did not respond to Reuter's request for comment.

The Democratic-controlled US House of Representatives is investigating whether Trump abused his power by pressing Ukraine to carry out investigations that would benefit him politically, including one targeting political rival Joe Biden.

Trump and his supporters have attacked the impeachment probe as politically motivated and called it a witch hunt.

A string of public impeachment hearings ended on Nov. 21, but House leaders have not ruled out conducting more hearings before they vote on whether to charge Trump. Additional witnesses could be called in a Senate trial to determine Trump's guilt or innocence.

Some high-ranking diplomats in the State Department and White House National Security Council officials have cooperated with the House investigation, defying Trump's orders.

Others, including McGhan, Bolton, Secretary of State Mike Pompeo, and Acting Chief of Staff Mick Mulvaney, have so far refused to testify.

Bolton and one of his former aides, Charles Kupperman, did not show up for closed-door depositions earlier this month. But Bolton has hinted that he has a story tell to investigators.

Earlier this month, Bolton's lawyer said in a letter to the House's counsel that his client was "personally involved" in events and meetings under investigation, and knew about "many relevant meetings and conversations" that lawmakers may not be aware of.

Bolton has joined a lawsuit filed by Kupperman seeking a court ruling on whether he must comply with a congressional subpoena.

That lawsuit, which is before US District Judge Richard Leon, could be dismissed on procedural grounds, potentially making the McGahn battle more significant.

McGahn's case "is a definitive ruling that the House is entitled to testimony" from current and former senior executive branch officials, Paul Rosenzweig, a former Justice Department lawyer, told Reuters.

"They are not parties to the case, but the principle applies," said Rosenzweig, now a senior fellow at the libertarian R Street Institute. "The question is if they even want to talk."

(Reporting by Jan Wolfe; additional reporting by Karen Freifeld; Editing by Noeleen Walder and David Gregorio)