Sen. John McCain John Sidney McCainCOVID response shows a way forward on private gun sale checks Trump pulls into must-win Arizona trailing in polls Nonprofit 9/11 Day bashes Trump for airing political ads on Sept. 11 anniversary MORE (R-Ariz.) on Tuesday expressed sorrow about the growing likelihood that Senate Republicans will invoke the "nuclear option" to end filibusters on Supreme Court justice confirmations.

“I think it’s a dark day in the history of the United State’s Senate,” McCain told CNN’s “New Day.”

“It’s going to happen, and it’s interesting that Republicans were dead seat against it when my former colleague Harry Reid Harry Mason ReidBottom line Filibuster fight looms if Democrats retake Senate Biden unites Democrats — for now MORE invoked it with the judges, but now it seems to be okay.”

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Sen. Chris Coons Christopher (Chris) Andrew CoonsConservative activist Lauren Witzke wins GOP Senate primary in Delaware Coons beats back progressive Senate primary challenger in Delaware Democrats back away from quick reversal of Trump tax cuts MORE (D-Del.) became the 41st Democrat to say he will oppose cloture on Supreme Court nominee Neil Gorsuch, giving Democrats enough backing to filibuster President Trump’s pick.

Republicans, who have said they will confirm Gorsuch “one way or another,” have signaled a willingness to change Senate rules to eliminate the filibuster on Supreme Court nominees so that only a 51-person simple majority is needed for confirmation.

Currently 60 votes are needed to approve cloture, and thus end a filibuster, on a nominee. Republicans control 52 seats in the chamber.

McCain on Tuesday urged caution about changing the rules, noting it will allow Democrats to more easily confirm their own court picks when they eventually hold the majority.

“If you can do this with 51 votes, what do you think the next nominee is going to be like?” McCain said. “And then what do you think is going to happen when the Democrats are in the majority in the Senate?”