John Dean, a star witness during Watergate who helped bring down the Nixon presidency, testified Monday that special counsel Robert Mueller has provided Congress with a "road map" for investigating President Donald Trump.

Dean, telling the House Judiciary Committee he wanted to provide some historical context, compared Mueller's findings to those of congressional investigators looking into the Nixon administration decades ago.

Dean, who was White House counsel during Richard Nixon's administration, was brought in as a star witness as House Democrats opened three days of sessions aimed at focusing public attention on the findings of the Russia investigation and the president's actions.

"We have a responsibility to do this work, to follow the facts where they lead," said Chairman Jerry Nadler, D-N.Y., as he gaveled in the hearing. He said the intent was to make certain "no president, Democrat or Republican, can ever act in this way again."

Ahead of the hearing, Nadler announced that the Justice Department has agreed to turn over some of the underlying evidence from Mueller's report, including files used to assess whether Trump obstructed justice.

In the first breakthrough in weeks of negotiations over the report, Nadler said the department will begin complying with the committee's subpoena on Monday and provide some of Mueller's "most important files." He said all members of the committee will be able to view them.

The Justice Department did not have an immediate comment.

In response to the agreement, Nadler said Democrats would not vote on holding Attorney General William Barr in criminal contempt, for now. Instead, the House will vote Tuesday on a resolution that would empower the Judiciary Committee to file a civil lawsuit for Mueller materials.

"We have agreed to allow the Department time to demonstrate compliance with this agreement," Nadler said in a statement. "If the department proceeds in good faith and we are able to obtain everything that we need, then there will be no need to take further steps."

The deal is unlikely to give Democrats all of what they were requesting — including an unredacted version of the report and secret grand jury testimony. But it is the first agreement that the Judiciary Committee has been able to strike with the department since the report was issued in April.

The slate of televised sessions on Mueller's report means a new, intensified focus on the Russia probe and puts it on an investigative "path" — in the words of anti-impeachment Speaker Nancy Pelosi — that some Democrats hope leads to Trump's impeachment. In doing so, they are trying to aim a spotlight on allegations that Trump sought to obstruct a federal investigation as well as his campaign's contacts with Russia in the 2016 election.

And they will lay the groundwork for an appearance from Mueller himself, despite his stated desire to avoid testifying.

Monday's hearing is the start of three days of Russia-related action on Capitol Hill. The House Intelligence Committee on Wednesday intends to review the counterintelligence implications of the Russian meddling. Mueller said there was not enough evidence to establish a conspiracy between the Trump campaign and Russia, but he said he could not exonerate Trump on obstruction.

On Tuesday, the House has scheduled the vote to authorize lawsuits against Barr and former White House counsel Donald McGahn for failing to comply with subpoenas from the Democratic-controlled House. The vote will put the full House on record approving the lawsuits, if leaders and committees decide they want to move forward with them.

Barr had defied a subpoena to provide an unredacted version of Mueller's report, along with underlying evidence. McGahn, who is frequently referenced in the report, has defied subpoenas to provide documents and testify before the House Judiciary Committee.

Language in the resolution also would make it easier for committee chairmen to take the Trump administration to court. The chairmen could take legal action to enforce subpoenas in the future without a vote of the full House, so long as the chairmen have approval from a five-person, bipartisan group where Democrats have the majority.

With Trump pledging that "we're fighting all the subpoenas," Democratic leaders want to avoid repeated floor votes on contempt resolutions that would detract from their legislative agenda.

The procession of hearings and votes in the week ahead is partly designed to mollify anxious Democrats who have pushed Pelosi, D-Calif., to begin impeachment proceedings immediately. Pelosi has rejected that option, preferring a slower, more methodical approach to investigating the president, including the court fights and hearings.

During a meeting with Nadler and other committee heads last week, Pelosi made the case that she would rather see Trump voted out of office and "in prison" than merely impeached, according to a report in Politico. A person familiar with the exchange confirmed the account to The Associated Press.

Educating the American public on what is in the Mueller report is a priority for Democrats, who believe Trump and his allies have created the public impression that the report said there was no obstruction of justice. Trump has made that assertion repeatedly, echoing Barr's judgment that there was not enough evidence in the report to support a criminal obstruction charge. Mueller said in the report that he could not exonerate Trump on that point.

The special counsel did not find evidence to establish a criminal conspiracy between Trump's campaign and Russia. But the report details multiple contacts between the two.

Republicans are poised to defend the president at the hearings and challenge Democrats on the decision not to open impeachment hearings.

Georgia Rep. Doug Collins, the top Republican on the House Judiciary Committee, sent Nadler a letter Friday calling the upcoming hearing a "mock impeachment hearing" and warning Democrats to be civil when speaking of the president.

Collins said in the letter that outside of impeachment proceedings, "it is out of order for a member of Congress, in debate, to engage in personalities with the president or express an opinion, even a third party opinion, accusing the president of a crime. The rules are clear on this point."