Sen. John McCain John Sidney McCainCindy McCain endorses Biden: He's only candidate 'who stands up for our values' Biden says Cindy McCain will endorse him Biden's six best bets in 2016 Trump states MORE is quickly walking back his statement that Republicans would automatically oppose any potential Supreme Court nominee from Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE.

Rachael Dean, a spokeswoman for the GOP senator, said that while McCain "believes you can only judge people by their record" and the Democratic presidential nominee "has a clear record of supporting liberal judicial nominees,” the Arizona senator would consider any Supreme Court pick sent to the chamber.

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"Senator McCain will, of course, thoroughly examine the record of any Supreme Court nominee put before the Senate and vote for or against that individual based on their qualifications as he has done throughout his career," she said.

The pivot comes hours after McCain pledged that Senate Republicans would unite against any Supreme Court nominee that a hypothetical President Clinton would try to get confirmed.

"I promise you that we will, we will be united against any Supreme Court nominee that Hillary Clinton — if she were president — would put up," the Arizona Republican told a Philadelphia radio station on Monday. "This is why we need the majority."

Republicans have put the late Justice Antonin Scalia's Supreme Court seat at the center of their push for winning the White House and keeping control of Congress, stressing that whoever fills the vacancy could decide the direction of the court for decades. They've also refused to consider Merrick Garland, President Obama's nominee.

Republicans are defending 24 Senate seats. To win control of the Senate, Democrats need to pick up five seats, or four if Clinton is in the White House.

McCain also cast doubt Monday on whether GOP nominee Donald 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 would be "superior" to Clinton because of his potential Supreme Court nominees, saying, "I don't know because I hear him saying a lot of different things."

McCain is up for reelection and is leading in the polls by an average of 16 percentage points, according to Real Clear Politics. He revoked his endorsement of Trump earlier this month.

But Trump has earned praise from some conservatives for floating roughly 20 names, including Sen. Mike Lee (R-Utah), as potential Supreme Court nominees should he win the White House.

McCain's initial comments were a break from pledges by some of his Senate GOP colleagues that they will consider— though not necessarily support — any Supreme Court nominee that the next president submits.