President Donald Trump lashed out at House Democrats and former White House Counsel John Dean III, calling him a “sleazebag attorney,” in advance of his testimony before the House Judiciary Committee Monday afternoon.

The president took to social media reiterating his claims of “no collusion” and “no obstruction,” and tweeted, “The Dems were devastated - after all this time and money spent ($40,000,000), the Mueller Report was a disaster for them. But they want a Redo, or Do Over. They are even bringing in @CNN sleazebag attorney John Dean.”

Dean was special counsel to former President Richard Nixon and in 1973 testified before the House Judiciary Committee, contradicting much of the official narrative there was no cover-up by the White House in the wake of a break in at Democratic National headquarters in the Watergate Hotel. His testimony led to Nixon’s resignation in advance of impeachment proceedings.

Dean's appearance Monday at a hearing convened by House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., is billed as “Lessons from the Mueller Report: Presidential Obstruction and Other Crimes.”

Dean, a regular contributor to CNN, has been critical of the Trump administration. He said early Monday on the network he would draw comparisons between White House actions documented in the Mueller Report and the Watergate scandal.

“I’m clearly not a fact witness, but I hope I can give them some context and show them how strikingly like Watergate what we’re seeing now . . . is,” Dean said.

In a public statement May 29, special prosecutor Robert Mueller said his report did not recommend charges against Trump because of a long-standing Justice Department policy that a sitting president cannot be indicted. Mueller, however, repeated a statement from his report that his legal team would have clearly exonerated Trump of obstruction if it could have.

Attorney General William Barr made a determination Trump’s actions did not warrant charges of obstruction, but he also admitted he had not reviewed the underlying documentation accompanying the report before making that determination.

About 60 congressional members, including one Republican, have called for the start of impeachment hearings. That is a fraction of the 435-member chamber. Speaker of the House Nancy Pelosi, D-Calif., has cautioned against rushing to impeachment, and instead has called for allowing more information, if any, to surface.

For his involvement in Watergate, Dean pleaded guilty to obstructing justice, was disbarred and spent four months in federal prison. House Republicans already were attacking his credibility in advance of the presidential tweets.

Dean was ordered by the White House not to testify before Congress but chose to do so rather than defy a congressional subpoena, in stark contrast to some Trump officials.