Sen. Orrin Hatch, R-Utah, said firing special counsel Robert Mueller would spark a crisis and could lead to the impeachment of President Donald Trump.
Hatch made his comments in a column in The Wall Street Journal.
"I believe it is in President (Donald) Trump’s best interest to allow the investigation to run its course, because I believe it will vindicate him," Hatch said. "It is in the country’s best interest, because it will provide definitive answers to questions that have embroiled our politics now for over a year.
"Firing Mr. Mueller would be a grave error. It would trigger a crisis, possibly even impeachment. It would threaten many of the administration’s accomplishments and make continued progress virtually impossible."
Still, Hatch said he opposes a bill before the Senate Judiciary Committee, designed to stop Trump from firing Mueller.
"From the beginning, I’ve said — including to the president — that Mr. Mueller’s investigation must be allowed to run its course," Hatch noted. "But I will vote against the bill, because it is unconstitutional.
"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."
He said his support for independent prosecutors in the past was a mistake.
"Freed from political accountability and meaningful oversight, independent prosecutors become a law unto themselves," he said. "They rove about seeking charges to bring to justify their existence."
Instead of supporting the bill, Hatch said he will back a resolution "to convey to the White House the sense of the Senate that Robert Mueller should be left to complete his work.”
"What I will not do — and what I urge my colleagues to reject — is subvert our constitutional design in favor of momentary urgencies," he said.