Actually, that wasn’t the most horrifying thing to me. The most horrifying thing was the questioner’s suggestion that Muslims ought all to be deported from the United States followed by Mr. Trump’s failure to take a stand against such a bigoted and essentially fascistic proposal:
http://time.com/4039658/trump-obama-muslim/
It compares very poorly to Senator McCain’s response, in a somewhat similar case, back in 2008.
But that’s neither here nor there: The question was appalling, and Mr. Trump’s answer didn’t reassure.