Why can't Donald Trump handle Megyn Kelly?

This feud has gotten ridiculous. Republican front-runner and businessman Donald Trump is now threatening to boycott the upcoming GOP debate if host Fox News doesn’t remove Megyn Kelly as a moderator.

I don’t usually like the argument that takes the form of, “if candidate can’t stand up to X, how can they stand up to the Islamic State?” But I do wonder how Trump will be able to handle anyone as president if he can’t take the sort of pointed questions about his weaknesses that originally soured him on Kelly.