Several of the most popular porn sites are in the Alexa top 100 (ish) in the U.S. You don't get that kind of traffic without having a massive number of Americans watching porn regularly.

There's a perception that watching porn is taboo, but that's probably because it's not a socially acceptable topic of conversation. Everyone does it or has done it.

There is absolutely no way that this idiotic pledge of his can have a net positive gain for him. If anything, this will probably encourage otherwise non-voters to vote against him.