Over the course of the Election Nate Silver has predicted everything from a certain Hillary blowout, to a tight race that Trump could win. Unless Trump wins in a landslide he can state that he correctly predicted the outcome at some point in time. Even if Trump does win in a landslide, he can say that his models were probabilistic and there was always a nonzero probability of that outcome, so technically he was right.
It's a nice con game that has catapulted him to the status of premiere pundit.