GOP Sen. Orrin Hatch Orrin Grant HatchBottom line Bottom line Senate GOP divided over whether they'd fill Supreme Court vacancy MORE (Utah) warned on Wednesday that a "crisis" could be triggered if President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE fires 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, potentially including impeachment.

"Firing Mr. Mueller would be a grave error. It would trigger a crisis, possibly even impeachment," Hatch, a former chairman and current member of the Senate Judiciary Committee, wrote in a Wall Street Journal op-ed.

He added that letting Mueller finish his probe into the 2016 election and potential collusion between Moscow and Trump's campaign is in the country's and Trump's "best interest."

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Firing Mueller, a former FBI director who is widely respected in Washington "would threaten many of the administration’s accomplishments and make continued progress virtually impossible," Hatch wrote.

Hatch's op-ed comes ahead of a vote Thursday in the Judiciary Committee on legislation that would limit Trump's ability to fire Mueller.

The bill would make it so only a senior Justice Department official could fire Mueller. It would also let Mueller or any other special counsel challenge their firing. They would be reinstated if a court determined it wasn't for "good cause."

Hatch is expected to vote against the bill because he believes it's unconstitutional. He's also repeatedly told reporters that he doesn't believe Trump will ultimately fire the special counsel.

"I endorse the message the special-counsel bill is meant to send. But I take seriously the responsibility to ensure that the laws Congress passes comport with the Constitution," Hatch added in his Wall Street Journal op-ed.

Trump has lashed out at Mueller following the FBI's raid on the office, home and hotel room of his personal lawyer, Michael Cohen. The raid was sparked, in part, by a referral from Mueller's team.

But Trump downplayed speculation that he wanted to fire Mueller, despite reports that he has previously tried but ultimately backed down.

"If I wanted to fire Robert Mueller in December, as reported by the Failing New York Times, I would have fired him. Just more Fake News from a biased newspaper!" he tweeted earlier this month.