Trump describes himself as \'very innocent\' hours before potentially damaging Mueller testimony to Congress

President Trump and special counsel Robert S. Mueller III.Jabin Botsford/The Washington Post via Getty Images; Win McNamee/Getty Images

President Donald Trump described himself as "very innocent" in a tweet published hours before former special counsel Robert Mueller is due to testify before Congress about the findings of his probe into allegations of collusion and obstruction by the president. 

Early on Wednesday morning, Trump wrote: "So Democrats and others can illegally fabricate a crime, try pinning it on a very innocent President, and when he fights back against this illegal and treasonous attack on our Country, they call It Obstruction? Wrong! Why didn't Robert Mueller investigate the investigators?" 

He declined to reach a conclusion on charges that Trump attempted to obstruct his investigation. 

"If we had had confidence that the president clearly did not commit a crime, we would have said so," remarked Mueller  in May, at his single press conference on the report. 

Democrats are widely expected to closely question Mueller on this part of his report.

The president has previously denied claims by former White House counsel Don McGahn in the Mueller report, in which he claimed the president had ordered him to fire Mueller then lie to the press about the order. 

Late Tuesday, the president had crticised a decision by the committee to allow Mueller's deputy, Aaron Zebley, to appear alongside him during his testimony. 

"His lawyer represented the "basement server guy" who got off free in the Crooked Hillary case. This should NOT be allowed. Rigged Witch Hunt!" tweeted the president.