Sen. John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) says GOP delegates should be allowed to vote for any candidate they want to at the Republican National Convention next month, effectively siding with a movement among delegates to block presumptive nominee Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE.

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"I think it's up to every delegate to make up their own minds," McCain told The Weekly Standard on Tuesday. "I do not tell them what to do, I never have."

A group of delegates has been lobbying party officials to change convention rules in order to unbind them from voting for Trump.

Last week, Colorado delegate Kendal Unruh proposed a rule in a letter to the convention’s rules committee that would have freed the delegates to vote their conscience.

“If any such delegate notifies the secretary of his or her intent to cast a vote of conscience, whether personal or religious, each such delegate shall be unbound and unconstrained by these rules on any given vote, including the first ballot for the selection of the president of the United States, without the risk of challenge, sanction or retribution by the Republican National Committee (RNC),” Unruh wrote.

McCain, who is locked in a tight reelection race and has mostly avoided calling out Trump, did not say whether he supported the delegate uprising.