President Obama delivered a blistering criticism of Donald Trump on Tuesday at the White House, accusing the GOP nominee of being wholly unfit to serve as commander in chief and asking Republicans why they are still backing him. Obama said Trump “keeps on proving” that he is unfit to be president, especially in light of his criticisms of a Gold Star family that was featured prominently at last week’s Democratic convention in Philadelphia. “The notion that he would attack a Gold Star family that had made such extraordinary sacrifices on behalf of our country, the fact that he doesn’t appear to have basic knowledge around critical issues in Europe, in the Middle East, in Asia means that he’s woefully unprepared to do this job,” the president said at a joint news conference with the prime minister of Singapore. He also went after Republicans who have criticized Trump’s comments and actions but still support him. “The question you have to ask yourself is, if you are repeatedly having to say in very strong terms that what he has said is unacceptable, why are you still endorsing him?” Obama said.