Rep. Devin Nunes said he is expecting "the worst" from former special counsel Robert Mueller's testimony next week.

On Monday, the California Republican suggested there is a back channel Democrats have with Mueller to work out "a few little sound bites" that they could use to their advantage. Asked to expound upon that warning on Wednesday, Nunes said just one phrase from Mueller could be used to fuel a push for impeaching President Trump.

"I really expect the worst because Bob Mueller does not have to show up," Nunes told Fox News' Martha MacCallum. "So he’s doing this on his own free will. That tells me the last time he operated on his own free will, everyone forgets, [Attorney General William] Barr came out with a memo, was very clear about the decision that he had made, and then a few days later Mueller decided on his own to go out and hold a nine-minute press conference."

In his only public statement so far on the Russia investigation at the end of May, Mueller indicated he had no desire to testify about his work, let alone do it publicly. "The report is my testimony," he said. Mueller only agreed to testify after he was subpoenaed.

Mueller will testify in an open setting before the House Judiciary and Intelligence Committees on July 24.

Nunes, the House Intelligence Committee ranking member, reiterated that he is "very concerned," adding, "I think we should expect the worst because he only has to say a couple things and the rest of the media — I'm not saying you here at Fox, but 90% of the media will take one little phrase and run with it and try to run towards impeachment."

The Democratic-led House rejected a resolution to bring articles of impeachment in a vote on Wednesday, but momentum is building as Trump faces racism allegations for his controversial tweets aimed at four minority congresswomen.

Mueller’s report, released by the Justice Department with redactions in April, concluded that Russia interfered in the 2016 election but did not establish that any members of the Trump campaign criminally conspired with the Russians in these efforts. Mueller did not reach a conclusion on obstruction of justice, but Barr and Deputy Attorney General Rod Rosenstein concluded there was insufficient evidence for such a crime.

Nunes has called Mueller's investigation an "obstruction of justice trap."