WASHINGTON — Attorney General William Barr's snub of House Democrats on Thursday has triggered an all-out war between the White House and Congress, pushing the House closer to holding the nation's top law enforcement official in contempt of Congress and prompting Speaker Nancy Pelosi to liken President Donald Trump to President Richard M. Nixon.

The almost daily confrontations between the two branches of government increase the pressure on Pelosi, D-Calif., to initiate impeachment proceedings against Trump, a politically fraught move that she has resisted in the absence of strong public sentiment and bipartisan support. Many Democrats argue that the 2020 election is the best means to oust the president.

But Democrats are infuriated with Barr, who refused to testify Thursday at the House Judiciary Committee's scheduled hearing on his handling of special counsel Robert Mueller's report, and Trump's defiance in the face of multiple congressional requests for documents and witnesses. Democrats cast the administration's unwillingness to cooperate as a threat to democracy with far-reaching implications.

“Ignoring subpoenas of Congress, not honoring subpoenas of Congress — that was Article III of the Nixon impeachment,” Pelosi said of Trump in a private meeting with colleagues, according to notes taken by an individual present for the remarks. “This person has not only ignored subpoenas, he has said he's not going to honor any subpoenas. What more do we want?”

Pelosi escalated her rhetoric this week as more Democrats press for tough steps to counter the president.

Republicans have insisted that Democrats were simply intent on targeting Trump, unwilling to accept a lengthy investigation that found no criminal conspiracy between the Trump campaign and Russia.

“I think the Democrats are substantially overreaching,” said Rep. Mike Simpson of Idaho, one of the few House Republicans who has criticized Trump in the past. “The problem is they tried to convince the American people that he colluded with the Russians for the last two years and now we find out that's false. … And it's like, 'OK, we've got to save our bacon. We've got to find something!' And that's what they're doing.”

Republican lawmakers also rebuffed the Democrats' argument that their moves were to safeguard the powers of Congress and that the GOP had a constitutional responsibility to join them. Trump's congressional allies — loath to say anything against him — rallied to his side instead.

Appearing at a Washington Post Live event Thursday morning, House Minority Leader Kevin McCarthy, R-Calif., essentially accused U.S. law enforcement of treason during the investigation of Russian interference in the 2016 presidential election.

"Their actions are a coup," McCarthy said, suggesting anti-Trump bias influenced the origins of the probe. "I do not believe they were abiding by the rule of law."

The tensions between the Trump administration and Congress could come to a head as early as next week, when House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., said his panel will probably adopt a contempt citation against Barr unless he provides the full, unredacted Mueller report.

Nadler had subpoenaed the document and imposed a Wednesday deadline. But Barr has refused to turn it over, with Justice Department officials arguing that the request "is not legitimate oversight." Barr also declined to testify Thursday, rejecting the Democrats' plans to have a counsel question him alongside lawmakers.

Democrats cast the snub as more than one witness rebuffing a congressional committee, but rather a threat to democracy that would reverberate long after Trump left office. The president has vowed to "fight all the subpoenas" from Democrats, sued to block compliance by accounting firms and banks, and instructed former and current aides to ignore the repeated requests from Capitol Hill.

"He's trying to render Congress inert as a separate and coequal branch of government," Nadler said. "If we don't stand up together, today, we risk forever losing the power to stand up to any president in the future."