John McCain vows to block any Hillary Clinton Supreme Court nominee

John McCain made the case for a GOP Senate majority – and offered Republicans an opportunity to walk away from Donald Trump – when he told a Philadelphia radio station he would work to block any Supreme Court nominee put forward by a President Hillary Clinton.

"I promise you that we will be united against any Supreme Court nominee that Hillary Clinton, if she were president, would put up," the Arizona Republican told 1210 WPHT Philadelphia Monday morning, in an appearance arguing in favor of re-electing Sen. Pat Toomey, R-Pa. "I promise you. This is where we need the majority and Pat Toomey is probably as articulate and effective on the floor of the Senate as anyone I have encountered."

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Both McCain and Toomey are facing competitive challenges to re-election to their Senate seats, and the outcomes of their races could determine which party holds the majority in the upper chamber next year.

Republicans currently hold 54 seats in the Senate while Democrats hold 46, including two independents who caucus with them. Should Clinton be elected on Nov. 8, Democrats would need to flip just four of the seats currently in GOP hands in order to take a majority.

While McCain appears to hold a comfortable lead over Democratic Rep. Ann Kirkpatrick in his re-election bid, Toomey is essentially tied in polls with Democrat Katie McGinty.

Toomey has so far refused to endorse Trump.

"I am not endorsing him and I remain unpersuaded," Toomey said last week.

Several of his GOP colleagues, including McCain, Sen. Kelly Ayotte of New Hampshire and Rep. Joe Heck, running for the seat being vacated by Sen. Harry Reid, D-Nev., dropped their support of their party's nominee after the publication of a 2005 "Access Hollywood" video in which Trump bragged about groping women without consent.

"The way I look at it is we have two terrible choices, and I think many Pennsylvanians view it like this," Toomey told reporters after a breakfast on Tuesday. "This is not, ultimately, a referendum on anyone. It's a choice. It's a bad choice."

As Trump has sunk in the polls – most national and swing state surveys show him with a very narrow path to winning the White House – many Republicans further down the ballot have begun to position themselves as a check on a Clinton presidency.

But McCain went further than most, making an explicit appeal to Republican voters who dislike Trump but have said they would back him because the next president is likely to see several Supreme Court vacancies during his or her term. The partisan makeup of the court, already short a member since the death of Justice Antonin Scalia in February and split evenly between conservative and liberal justices, could be shifted ideologically for generations during the next administration.

But McCain's plan has a serious flaw: If Clinton wins and Republicans do end up in the minority, McCain and his colleagues may find themselves without the ability to do anything to stop her nominees.

Since capturing the majority in the 2014 midterms, Republicans frustrated with Democrats blocking their agenda have proposed abolishing the filibuster, which allows a minority of senators to block legislation or appointments from advancing through the chamber's byzantine procedures that often require a 60-member supermajority to move to a final vote.

In 2013, Democrats changed the rules so most executive appointments no longer needed to clear the 60-vote threshold to pass. Should the Democrats regain the majority this fall, they could further amend the rules to include Supreme Court.