WASHINGTON — Pro-impeachment Democrats are struggling to make their case for ousting President Donald Trump to a wary public, with the Justice Department suddenly signaling a willingness to cooperate with Congress and the House's first hearing on Robert Mueller's report veering into more of a historical lesson on Watergate.

Attorney General William Barr reached a deal with the House Judiciary Committee on Monday to allow lawmakers to view underlying documents from Mueller's nearly two-year investigation into Russian interference in the 2016 presidential election and whether Trump obstructed the probe.

The last-minute deal — struck a day before a scheduled House vote on holding Barr in civil contempt — appeared to undercut the Democratic argument that only an impeachment inquiry could force an uncooperative administration to comply, at least momentarily.

Hours later, the first hearing since the April 18 release of the redacted Mueller report didn't produce a blockbuster moment that could change public sentiment in favor of impeachment. Former White House counsel John Dean testified about the parallels between Trump and his former boss, President Richard Nixon — though he acknowledged that he was not a "fact witness."

"It's quite striking and startling that history is repeating itself and with a vengeance — so that's why I've spoken out," Dean told the Judiciary Committee.

But committee Republicans repeatedly mocked Democrats for bringing in Dean — a star witness from nearly a half century ago who has a CNN contract — and several other former U.S. attorneys who have television deals and have criticized Trump. None was involved in Mueller's investigation.

"Here we sit today in a hearing with the ghost of Christmas past because the chairman of the committee has gone to the speaker of the House and sought permission to open an impeachment inquiry and she said no," said Rep. Matt Gaetz, R-Fla., who asked Dean how much he earned in his CNN contract; Dean wouldn't say.

Trump, in brief remarks at the White House, dismissed both Dean, whom he had called a "sleazebag" in a tweet, and the notion of impeachment.

Dean has "been a loser for many years," the president said. "When you look at past impeachments, whether it was President Clinton, or I guess President Nixon never got there — he left. I don't leave. Big difference."

Privately, several Democrats said they agreed with the GOP's harsh assessment, wondering why Dean was called in the first place. The lawmakers and aides spoke on the condition of anonymity to freely discuss private conversations.

The hearing underscored the problems Democrats face in trying to draw attention to Mueller's findings as Trump repeatedly blocks his former White House aides from testifying and cooperating with requests for documents. Unlike Dean, who turned on Nixon and testified in the 1970s, Donald McGahn, Trump's former White House counsel, has refused to appear because the White House instructed him not to testify.

Mueller has also refused so far to agree to a date to appear publicly, privately expressing worries about being used politically by partisans on both sides. Consequently, Democrats have struggled to create a blockbuster moment like the one that made Dean famous and ultimately brought down a president.

Absent a compelling witness, Democrats who favor impeachment have found it difficult to move public sentiment — and convince a reluctant Speaker Nancy Pelosi, D-Calif., who has said the House will not launch impeachment proceedings unless Americans support the move.

While an increasing number of Democratic lawmakers and 2020 presidential hopefuls are calling for impeachment, a majority of the general public still does not support it.

A recent CNN poll released the last week of May found that 41% of the public supports proceedings while 54% does not. Another Fox poll from May similarly found 42% supporting and 50% opposed. A mid-May Monmouth poll found that public sentiment was going the opposite way, with 39% supporting impeachment, a dip from March when the same study found that 42% did.

Further undermining the push for impeachment was the Justice Department's deal with congressional investigators. Under the agreement, the Judiciary Committee will have access to interview notes, firsthand accounts and other evidence, according to Chairman Jerrold Nadler, D-N.Y.

It was unclear whether the material related to whether the president obstructed the Mueller inquiry would provide new details that could sway public opinion and lawmakers skeptical about an impeachment proceeding that likely would end with Trump's acquittal in the Republican-led Senate.

Rep. Jamie Raskin, D-Md., a member of the committee, said lawmakers had not been told precisely which materials the department was making available, but he said he did not expect key records, including grand jury testimony, to be included.

In reaching the deal, Nadler announced that he would not move to hold Barr in criminal contempt of Congress. However, the House is scheduled to vote Tuesday to authorize the Judiciary Committee to take Barr to civil court to enforce a subpoena for the underlying documents should they prove insufficient to their investigations. The measure, if passed, would also allow the House to sue McGahn to try to force him to testify.

In his opening remarks, Dean said the last time he testified before the House Judiciary Committee was July 11, 1974, nearly 45 years ago. Seven of the committee's 41 members weren't even born at that time, including Gaetz, who told Dean, "you sit before us here with no knowledge of a single fact of the Mueller report on a hearing entitled 'Lessons of the Mueller Report.' "

Committee Democrats repeatedly cited sections of the Mueller report and the former special counsel's explanation that his office could not consider whether to charge Trump with a crime because of a long-standing Justice Department opinion that a sitting president cannot be indicted. Mueller, in public remarks May 29, repeated a line in his report explaining that his team would have exonerated Trump of obstruction if it could have.

Democrats asked Dean about the significance of Trump calling McGahn and requesting that he find a way to oust Mueller, or the president leaning on Corey Lewandowski to pressure then-Attorney General Jeff Sessions to rein in the special counsel.

Rep. Sheila Jackson Lee, D-Texas, for instance, asked Dean why McGahn would have been so "perturbed" by Trump's weekend call to ask McGahn to get rid of Mueller.

"He was very aware that firing the special counsel would be equivalent to the Nixon Saturday Night Massacre," Dean said, later describing the October 1973 series of events in which the top two Justice Department officials resigned rather than follow Nixon's orders to fire special prosecutor Archibald Cox. "And so he stepped away from it and didn't want any part of it."

Democrats on the committee have been trying to highlight the findings of the 448-page, redacted report, aware that most Americans have not read the document and are unfamiliar with the findings.

That was the main purpose for bringing in Dean, who discussed similarities he saw between the two presidents, particularly on the matter of pardons and whether they were used to obstruct justice.

“In many ways, the Mueller report is to President Donald Trump what the so-called Watergate road map … was to President Richard Nixon,” said Dean, whose congressional testimony in 1973 ultimately led to Nixon’s resignation. “Special counsel Mueller has provided this committee with a road map.”

House Republicans tried to discredit Dean as a witness, questioning his role in the Watergate scandal knowing that Dean pleaded guilty to obstructing justice, later was disbarred and was imprisoned for four months.