John McCain warned Donald Trump on Monday that his feud with the Muslim father of a slain U.S. Army captain is putting him on even shakier ground with Republican voters, and Trump needs to set a much better example if he hopes to win GOP votes.

“Arizona is watching,” McCain warned in a statement. “It is time for Donald Trump to set the example for our country and the future of the Republican Party. While our party has bestowed up on him the nomination, it is not accompanied by unfettered license to defame those who are the best among us.”