Story highlights In a speech at a Federalist Society luncheon, he told the audience, "This is not my party"

Will has been a harsh critic of Trump in the past

Washington (CNN) George Will, the conservative commentator and columnist, said Sunday that he changed his voter registration to "unaffiliated" 23 days ago and has left the Republican Party because of Donald Trump.

"After Trump went after the 'Mexican' judge from northern Indiana then (House Speaker) Paul Ryan endorsed him, I decided that in fact this was not my party anymore," Will said on "Fox News Sunday."

Trump attacked Will on Twitter over his decision to leave the GOP Sunday morning, writing: "George Will, one of the most overrated political pundits (who lost his way long ago), has left the Republican Party. He's made many bad calls."

George Will, one of the most overrated political pundits (who lost his way long ago), has left the Republican Party.He's made many bad calls — Donald J. Trump (@realDonaldTrump) June 26, 2016

Will responded on "Fox News Sunday," saying: "He has an advantage on me, because he can say everything he knows about any subject in 140 characters and I can't."

He said he'd joined the Republican Party in 1964, inspired by Arizona Sen. Barry Goldwater, a founder of the conservative movement and a key figure in the party then.

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