WASHINGTON (Reuters) - Democrats intensified their pressure on President Donald Trump’s administration on Thursday as U.S. House Speaker Nancy Pelosi accused Attorney General William Barr of committing a crime by lying to lawmakers and a key committee chairman threatened to hold Barr in contempt of Congress.

Even as Democratic lawmakers accused the Trump administration of a growing attack on U.S. democracy and the authority of Congress, the White House showed no sign of backing down. White House legal counsel Emmet Flood said in a defiant letter that Trump had the right to tell advisers not to testify to congressional panels on the findings of Special Counsel Robert Mueller’s Russia inquiry.

The dueling statements marked a sharp escalation in the conflict between the White House and Democrats who control the House of Representatives. With Trump seeking re-election next year, Democrats are weighing whether to try to remove the Republican president from office using the impeachment process while pressing forward with demands for information on his taxes, businesses and other topics.

Shortly after Barr refused to appear before the House Judiciary Committee, Pelosi accused him of lying to lawmakers about interactions with Mueller after the special counsel ended a 22-month investigation into Russia’s efforts to interfere in the 2016 U.S. election to boost Trump’s candidacy.

“That’s a crime,” Pelosi, the top Democrat in Congress, told reporters, referring to Barr’s congressional testimony.

Justice Department spokeswoman Kerri Kupec called Pelosi’s allegation “reckless, irresponsible and false.”

Democrats have accused Barr of misleading Congress by testifying in April he was unaware of any concern by the special counsel’s team about Barr’s initial March 24 characterization of the report, an account that led Trump to claim full exoneration. Barr failed to mention a March 27 letter he got from Mueller complaining that Barr’s March 24 account did not “fully capture the context, nature and substance of this Office’s work.”

Judiciary Committee Chairman Jerrold Nadler threatened to hold Barr in contempt of Congress if he does not provide a full, unredacted copy of Mueller’s report and the underlying evidence, as the panel has requested by a subpoena that had a Wednesday deadline. That could potentially lead to legal steps against the top U.S. law enforcement official.

Barr released Mueller’s report on April 18, with some parts blacked out to protect sensitive information.

Several Democrats have called on Barr, whom Trump appointed after firing Jeff Sessions as attorney general, to resign.

Pelosi and other House Democrats previously had cautioned against launching the impeachment process, which would begin in the House but would face long odds of success in the Republican-controlled Senate and could alienate voters ahead of the 2020 presidential election.

But Pelosi said the Trump administration was continuing to ignore congressional subpoenas and noted that Congress launched impeachment proceedings against President Richard Nixon after he resisted similar demands. Nixon resigned in 1974 over the Watergate scandal.

‘OBSTRUCTION OF JUSTICE’

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Pelosi said Trump’s “blanket statement that he’s not going to honor any subpoenas is obstruction of justice.”

The White House signaled little appetite to cooperate.

Trump told Fox News in an interview on Thursday he was not inclined to let former White House counsel Don McGahn testify before congressional committees. Nadler has issued a subpoena for McGahn to testify in its investigation of possible obstruction of justice by the president.

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Trump told Fox News that McGahn had already spoken to Mueller’s team for 30 hours and allowing him to testify to Congress would open the door to others being called.

“I would say it’s done,” Trump said.

Flood reiterated that point in a letter seen by Reuters, saying Trump’s decision to let advisers cooperate when Mueller was conducting his investigation did not extend to congressional oversight investigations now that the inquiry had been completed.

Flood also said Mueller’s 448-page report suffered from “an extraordinary legal defect” by failing to determine whether Trump had committed the crime of obstruction of justice.

Mueller “instead produced a prosecutorial curiosity - part ‘truth commission’ report and part law school exam paper,” Flood wrote to Barr in a letter dated a day after the report was released.

Democrats have argued Trump waived the right to assert executive privilege - which allows a president to withhold information about internal executive branch deliberations from other branches of government - by allowing advisers to cooperate extensively with Mueller.

Barr canceled his House testimony after clashing with Nadler over the hearing’s format, particularly having staff lawyers question him in addition to committee members. Nadler said he would move forward with a contempt citation as soon as Monday.

“The very system of government of the United States - the system of limited power, the system of not having a president as a dictator - is very much at stake,” Nadler told reporters after a 15-minute committee session held in place of Barr’s appearance.

Democrats have said they may issue a subpoena to try to force Barr to testify.

Barr spent four hours before a Republican-led Senate committee on Wednesday defending his handling of Mueller’s report and justifying Trump’s actions.

The report detailed extensive contacts between Trump’s 2016 presidential campaign and Moscow and the campaign’s expectation that it would benefit from Russia’s actions, which included hacking and propaganda to boost Trump and harm Democratic candidate Hillary Clinton. The report also detailed a series of actions Trump took to try to impede the investigation.

Mueller, a former FBI director, concluded there was insufficient evidence to show a criminal conspiracy and opted not to make a conclusion on whether Trump committed obstruction of justice, but pointedly did not exonerate him. Barr has said he and Rod Rosenstein, the Justice Department’s No. 2 official, then determined there was not enough evidence to charge Trump with obstruction.