President Donald Trump has slammed House Democrats as they prepare to hold hearings on special counsel Robert Mueller's investigation in a possible prelude to impeachment.

'For two years all the Democrats talked about was the Mueller Report, because they knew that it was loaded up with 13 Angry Democrat Trump Haters, later increased to 18,' Trump wrote on Twitter Sunday night.

'But despite the bias, when the Report came out, the findings were No Collusion and facts that led to No Obstruction,' he continued.

'The Dems were devastated - after all this time and money spent ($40,000,000), the Mueller Report was a disaster for them,' Trump said.

Trump called John Dean (right) a 'sleazebag' on Sunday. Dean, who was White House counsel for President Richard Nixon, is scheduled to testify in the House on Sunday

The president continues: '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!'

Dean, who was White House counsel for President Richard Nixon, is scheduled to testify on Monday before the House Judiciary Committee at a hearing on 'presidential obstruction and other crimes.'

With Mueller planning to head to the sidelines, Democrats will rely on Dean, now a CNN contributor critical of Trump, to try to make headlines.

Dean delivered riveting 1973 testimony that helped reveal the existence of White House tapes. He testified that he knew key details of the Watergate cover-up that would eventually force Nixon's resignation.

In the hearings this week, Democrats will intensify their focus on the Russia probe and pick up the pace on an investigative 'path' - in the words of Speaker Nancy Pelosi - that some of them hope leads to impeachment of the president.

In doing so, they are trying to draw the public's attention on the allegations that Trump sought to obstruct a federal investigation and they want to highlight 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 the spotlight.

Rep Jerrold Nadler, known to be an aggressive proponent of impeachment, will preside over Monday's Judiciary Committee hearing on 'presidential obstruction and other crimes'

The hearings will focus on the two main topics of Mueller's report, obstruction of justice and Russian election interference.

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 a vote to authorize contempt cases against Attorney General William Barr and former White House counsel Donald McGahn for failing to comply with subpoenas from the Democratic-controlled House.

Barr 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.

Pelosi has so far rejected immediate impeachment, preferring a slower, more methodical approach to investigating the president, including the court fights and hearings

Language in the resolution would make it easier for committee chairmen to take the Trump administration to court. Those 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 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 so far rejected that option, preferring a slower, more methodical approach to investigating the president, including the court fights and hearings.

During a meeting with the House Judiciary Committee chairman, New York Rep. Jerrold 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.