George F. Will, a conservative columnist and prominent Republican pundit for the past 40 years, said he has left the Republican Party because Donald J. Trump is the party’s presumptive presidential nominee.

Mr. Will revealed his decision on Friday in an interview with PJ Media. He said he had switched his party registration to unaffiliated this month, adding that Republicans should “grit their teeth” during a Hillary Clinton presidency and then hope to beat her in 2020.

“This is not my party,” Mr. Will said in a speech on Friday at the Federalist Society before the PJ Media interview.

Mr. Will has criticized Mr. Trump throughout his presidential run.

“Only he knows what he is hiding by being the first presidential nominee in two generations not to release his tax returns,” Mr. Will wrote in his Washington Post column on Wednesday. “It is reasonable to assume that the returns would refute many of his assertions about his net worth, his charitableness and his supposed business wizardry. They might also reveal some awkwardly small tax payments.”