Of course it makes him look at if he cares more about a personal vendetta than he does about the party or the ideas he espouses. As if he is, he is, that's the point. He's revealing who he is. This isn't some gaffe or accident. If it were something he threw off, and then realizes he was a little over the time, he had ample opportunity over the weekend to retract, to move away. Instead he doubled down. He widened the net of sort of non-Americans or people who aren't impartial because of their ethnicity beyond Mexican-Americans to now include Muslim.
This isn't a guy who has made a false step, of course he did. But the larger point is, he's revealing who he is. It is not just that those who have now decided to throw in and support him for party unity or whatever reasons have made a tactical mistake in getting behind him. They have to ask themselves, morally, is this the man you want to be the leader of your party? That's what's at stake here. That's why it's a bigger issue.