Chip Somodevilla/Getty Images Sen. John McCain said Monday that Republicans would be "united against" any nominees for the Supreme Court put forward by Hillary Clinton if she wins the presidency.

The main pretext Republican senators have offered for leaving open the Supreme Court seat of the late Justice Antonin Scalia is that the next president, not Barack Obama, should be the one to fill it.

But now that his party’s nominee, Donald Trump, seems headed for a loss in November, Sen. John McCain (R-Ariz.) appears to be changing his tune ― and may be signaling that more unprecedented obstruction is on the horizon if Hillary Clinton wins the White House.

“I promise you that we will be united against any Supreme Court nominee that Hillary Clinton, if she were president, would put up. I promise you,” McCain said Monday, according to CNN.

The senator made the comments during a Pennsylvania radio interview in which he threw support behind his colleague Pat Toomey, who is struggling in the polls and may be key to Republicans retaining control of the Senate.

“This is the strongest argument I can make” for Pat Toomey’s re-election, McCain said, and that is “so we can make sure there is not three places on the United States Supreme Court that will change this country for decades.”

Three justices will be in their 80s during the next administration, making the prospect of retirement and more vacancies likely.

The Arizona senator didn’t specify if Senate unification against any Supreme Court nomination by a President Clinton means not holding confirmation hearings or taking a vote on them at all ― as they have done to Obama’s choice, Merrick Garland, already the longest-waiting nominee in history ― or if it means voting them down no matter who the nominees are.

He also didn’t note whether other senators are in on this new strategy. But last week, Sen. Mike Lee of Utah indicated he might be ready to reject any name Clinton puts forward, under a theory that Democratic nominees to the high court don’t vote “independently” from party interests.

As with many other things this campaign season, none of this may matter. Later on Monday, McCain, through a spokeswoman, reversed course on his earlier remarks about future Clinton nominees and noted he’d “vote for or against that individual based on their qualification,” according to Talking Points Memo.

As for where Clinton and Trump stand on the Supreme Court, both candidates will likely be asked about it again at the third and final presidential debate on Wednesday, where Fox News’ Chris Wallace is expected to dedicate 15 minutes to the subject.

Ahead of the debate, Clinton has already offered a vision of what her nominees might look like, while Trump has drawn up a not-so-short shortlist of potential candidates that was strong enough to get constitutionalist Sen. Ted Cruz (R-Texas) to bow to the Republican nominee.

McCain walked back his comments Monday afternoon, and this article has been updated to reflect that.