WASHINGTON (Reuters) - Donald McGahn, the former White House counsel described in the Mueller report as repeatedly standing up to President Donald Trump, could become a star witness again if congressional Democrats get their way in their investigation of whether Trump used his office to obstruct justice.

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

Since the April 18 release of Special Counsel Robert Mueller’s report on Russian interference in the 2016 election and any ties to Republican Trump’s campaign, Democrats have seen McGahn as someone who could be as important as Mueller himself, according to a source familiar with the matter.

But the Democrats are likely to face Trump’s resistance. The Washington Post reported on Tuesday that the White House planned to oppose a subpoena by the House of Representatives Judiciary Committee for McGahn to testify.

Mueller’s 448-page partially blacked-out report portrayed McGahn as one of the few figures in Trump’s orbit to challenge him when he tried to shut down the investigation that has clouded his more than two years in the White House.

“Mr. McGahn has been touted as a man of integrity and he is a major witness in the Mueller report,” said Democrat Sheila Jackson Lee, a member of the Judiciary Committee.

The White House did not immediately comment on the Washington Post report, which said the White House would claim executive privilege, a legal doctrine allowing the president to withhold information about internal executive branch deliberations from other branches of government.

Trump said in a Tuesday interview with the Washington Post that White House lawyers had not “made a final, final decision” about whether they will cite executive privilege to prevent McGahn and other former and current officials from testifying.

“They testified for so many hours. They have all that information that’s been given,” Trump told the newspaper of the Mueller report and congressional Democrats.

McGahn’s attorney, William Burck, did not respond to requests for comment.

Democrats are particularly interested in hearing McGahn describe in his own words and in Congress an account in the Mueller report in which McGahn refused Trump’s instructions.

In June 2017, Trump called McGahn to say he should tell Deputy Attorney General Rod Rosenstein to remove the special counsel because he had conflicts of interest, the report said.

Trump also failed to get McGahn to dispute media reports that the president tried to fire Mueller, the report said.

“That, in itself, could be an obstruction of justice, as Mr. McGahn would be able to testify – that he was asked to do it and then asked not to tell anyone what he’d been asked to do,” Lee said.

SEEKING DOCUMENTS, TESTIMONY

Committee Chairman Jerrold Nadler, who has subpoenaed the U.S. Department of Justice to provide the unredacted Mueller report and underlying evidence, issued a subpoena on Monday for McGahn to provide the committee with documents by May 7 and testify on May 21.

But it was not clear that McGahn would comply, especially if the White House asserts executive privilege. Nor could Democrats predict how much the former White House counsel would be willing to discuss, even if he does testify.

On Tuesday evening, Nadler said: “The moment for the White House to assert some privilege to prevent this testimony from being heard has long since passed.”

The House of Representatives has the sole power under the U.S. Constitution to impeach the president, and any effort would be led by the judiciary panel.

Mueller’s report concluded that there was not enough evidence to establish that Trump’s campaign engaged in a criminal conspiracy with Moscow. The report outlined multiple instances, however, where Trump tried to thwart Mueller’s probe.

Mueller stopped short of concluding whether Trump could be prosecuted for obstruction of justice, a criminal charge that requires proof beyond a reasonable doubt.

Such a high standard would not apply to Democrats if they decided to bring impeachment proceedings.

In the days following the Mueller report’s release, McGahn came under attack from Trump’s personal attorney Rudolph Giuliani, who called into question the veracity of his statements to Mueller’s team of prosecutors.

“I would ask which of the three versions is McGahn standing by. There are three versions he gives of that account,” Giuliani told CNN over the weekend. “I’m telling you, he’s confused.”

A prominent elections lawyer, McGahn served as Trump’s campaign counsel before being named White House counsel in November 2016.

He played a pivotal role in helping Trump reshape the federal judiciary in a conservative direction and roll back regulations on a range of industries.