In this video, he says the racist comments about the judge were the last straw.

Asked if he hopes other Republicans join him in unendorsing Trump, the senator replied: "I do. I think we should send a strong message to the Donald that racism and bigotry are not going to be tolerated in the party of Lincoln."

But he's given other reasons too:


Mother Jones says "this might be the first time ever that a senator has un-endorsed a presidential candidate of his party."