This story was last updated on July 22 at 6:54 am.

A leading House Democrat says special counsel Robert Mueller will give "very substantial evidence" that will make the case for impeaching U.S. President Donald Trump.

"This is a president who has violated the law six ways from Sunday," House Judiciary Committee chairman Jerrold Nadler told Fox television on the weekend.

Legislators from Trump's Republican Party, however, predict a highly anticipated hearing this week will amount to nothing more than a rehash of previously published information.

Also speaking Sunday on Fox television, Congressman Doug Collins, the top Republican on the Judiciary Committee, accused Democrats of "going after things that we've already known."

Mueller is set to testify before two House committees Wednesday about his investigation into whether the Trump campaign colluded with Russia to meddle in the 2016 presidential election and if Trump obstructed justice in trying to derail the probe.

"We have to present, or let Mueller present, those facts to the American people...because the administration must be held accountable and no president can be above the law," Nadler said.

Mueller report conclusions



The Mueller report concluded there was not enough evidence to determine that Trump or his campaign colluded with Russia. But Mueller wrote he could not exonerate Trump of allegations of obstruction of justice, turning the matter over to Attorney General William Barr. Barr said he could find no evidence of obstruction.

Trump was highly critical of the Mueller investigation, but does say the report clears him of any alleged criminal activity.

FILE - Robert Mueller, then-special counsel probing Russian interference in the 2016 election, departs Capitol Hill following a meeting with lawmakers, in Washington, June 21, 2017.

Mueller has said he chose the words in his report very carefully and would not provide any other information in any public testimony.

But Nadler said Sunday he does not expect Mueller's appearance to be what he called a "dud."

"The president and the attorney general have lied to the American people about what was in the Mueller report...the president saying they found no collusion. That was not true, that it found no obstruction, that is not true."

Very specific questions



Nadler says lawmakers will ask Mueller some very specific questions about parts of the report.

"Look at page 344, paragraph two...does that describe obstruction of justice...did you find that the president did that, for example."

Republicans are upset at what they see as Democratic efforts to keep what they regard as a one-sided but over-and-done investigation of the president on the front pages.

"It's like going back and finding a book on the shelf that looks new and then all of a sudden you begin to read and you find 'wait, I've already read this before'," Collins said on Fox television.