A U.S. federal judge ruled late Monday that former White House counsel Donald McGahn must comply with a House subpoena for his testimony in the Trump impeachment inquiry.

Judge Ketanji Brown Jackson said the president "does not have the power" to excuse McGahn or any other current and former White House officials from testifying.

The Trump administration plans to appeal Jackson's ruling. A lawyer for McGahn said he would comply with the House subpoena unless a court imposes a stay pending appeal (temporarily suspending the judgment until a ruling on the appeal).

FILE - U.S. Secretary of State Mike Pompeo talks to journalists during a news conference during a NATO Foreign Ministers meeting at the NATO headquarters in Brussels, Nov. 20, 2019.

Others who have resisted testifying include Secretary of State Mike Pompeo, former National Security Adviser John Bolton, and acting Chief of Staff Mick Mulvaney.

Democrats looking into whether to impeach Trump for pressuring Ukraine to investigate 2020 presidential rival Joe Biden believe these senior officials can provide vital evidence.

McGahn was White House counsel until he resigned in October, 2018. His name prominently surfaced in former special counsel Robert Mueller's report on suspected collusion between the Trump campaign and Russian meddling in the 2016 presidential election.

FILE - Former special counsel Robert Mueller checks pages in the report as he testifies before the House Judiciary Committee hearing on his report on Russian election interference, on Capitol Hill, July 24, 2019.

According to the report, McGahn told investigators Trump pushed him to fire Mueller and then deny Trump made such a request

Mueller said he could not exonerate Trump on charges of obstruction of justice. Democrats pursuing impeachment are considering whether to include Trump's apparent attempt to get Mueller fired as part of their inquiry, believing that such an attempt could be considered obstruction.

A whistleblower's concern over Trump's July 25 telephone call asking Ukrainian President Volodymyr Zelenskiy to do a "favor" and open a corruption probe into Biden led to the impeachment inquiry.

Two weeks of public testimony from a number of current and former U.S. diplomats and officials — who said Trump withheld military aid to Ukraine in exchange for an investigation into Biden — appears to have strengthened the Democrats' case for impeachment.

Trump insists he did nothing wrong and calls the impeachment inquiry a hoax and a witch hunt. His Republican supporters say whatever Trump did, it does not reach the threshold for impeachment.

Chairman of the House Intelligence Committee Adam Schiff, D-Calif., questions former U.S. Ambassador to Ukraine Marie Yovanovitch before the House Intelligence Committee, Nov. 15, 2019.

Chairman of the House Intelligence Committee Adam Schiff said in a letter Monday to the entire House that the committee is writing its report.

"While we will continue with our investigative work and do not foreclose the possibility of further depositions or hearings, we will not allow the President or others to drag this out for months on end in the courts," Schiff wrote.

The report will go to the Judiciary Committee, which likely will draw up articles of impeachment against Trump.

While a Trump impeachment would more than likely be assured in the Democratically-controlled House, the president likely would survive a trial in the Republican-controlled Senate, where it takes a two-thirds majority to remove him from office.