Committee Republicans mocked Democrats for bringing in Dean - a name from a bygone era who has a CNN contract - and several other former US attorneys who have TV contracts. Representative Douglas Collins, the top GOP lawmaker on the panel, said if Democrats really cared about stopping Russia interference in future elections, the committee would be asking experts - not cable commentators - to testify.
"I can catch your testimony on TV!" Collins said to the witnesses before pivoting to Dean specifically: "This committee is hearing from the 70s and they want their star witness back."
He added: "Here we are again with priorities in this committee turned upside down."
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 were born after his testimony.
At the White House, Trump dismissed Dean and any notion of impeachment.
"John Dean's been a loser for many years," the President told reporters, adding: "You can't impeach somebody when there's never been a thing done wrong. When you look at past impeachments . . . there's a big difference, I don't leave."
The criticism underscores the problem Democrats face in trying to draw attention to Mueller's findings, particularly because Trump has blocked former White House aides from testifying. Mueller himself has also refused so far to agree to a date to testify publicly, privately expressing worries about being used politically by partisans on both sides.
Democrats have struggled to create blockbuster moments like the one where Dean turned on his former boss and helped bring down a president. Trump's former White House counsel Donald McGahn, in fact, has refused to testify because the White House told him not to.
Democrats convened the hearing two hours after the panel announced it reached a deal with the Justice Department to obtain "key evidence" related to Mueller's investigation into whether Trump obstructed justice.
Under the agreement, the panel will have access to interview notes, first-hand accounts and other evidence, according to Chairman Jerrold Nadler, who announced that he would not move to hold Attorney-General William Barr in criminal contempt of Congress.
The House tomorrow, however, will vote to authorise the panel to take Barr to civil court to enforce a subpoena for the underlying documents should the documents prove insufficient to investigations.
The 448-page, redacted Mueller report was released on April 18.
Earlier in the day, Trump lashed out at Dean, calling him a "sleazebag" ahead of his appearance at a House hearing.
In tweets, Trump also took aim at House Democrats for continuing to focus on the report by Mueller that details findings of his investigation into Russian interference in the 2016 presidential election as well as possible episodes of obstruction of the probe by Trump.
In tweets yesterday that he retweeted today, Trump claimed that Democrats were "devastated" by Mueller's findings.
"The Mueller Report was a disaster for them," Trump wrote. "But they want a Redo, or Do Over. They are even bringing in @CNN sleazebag attorney John Dean. Sorry, no Do Overs - Go back to work!"
Today's hearing, convened by Nadler, is billed as: "Lessons from the Mueller Report: Presidential Obstruction and Other Crimes." Besides Dean, two former US attorneys and a legal scholar are scheduled to appear.
Appearing on CNN, Dean said he would draw comparisons in his testimony between 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.
He said he was not bothered by Trump's tweets.
"He's called me nasty names before," Dean said. "It doesn't bother me in the slightest."
A growing number of Democrats have called for launching an impeachment inquiry against Trump, while House Speaker Nancy Pelosi has continued to counsel a more deliberate course.
