Republican strategist Alex Castellanos on Sunday warned President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE to "get good legal help now."

Castellanos said during a panel on ABC's "This Week" that it is hard to believe that special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE "is not going to dig up something in Trump’s complicated financial history to say 'Look, the president of the United States did this and it was wrong.' "

"And it’s hard to believe then that when Republicans lose the House in 2018, maybe by 40 or 50 seats, that House is not going to impeach him," he said.

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"And it’s also hard to believe that a U.S. Senate that’s going to be scared to death, though may still be in Republican hands, is not going to take a serious look when it has to deal with this president."

He directed a warning to Trump: "So get good legal help now, because the storm is coming."

The comments come as Mueller continues his investigation into Russia's election interference and possible ties between the Trump campaign and Russia.

Trump has repeatedly dismissed the Russia probe as a "witch hunt" and has denied collusion between his campaign and Moscow.