Aside from the obvious constitutional problems, it would seem like a stupid way to about the matter. People who consume science fiction are precisely the people likely to support space exploration. By taxing science fiction, less of it will be produced, less will be consumed, and the push to explore space will be decreased in the end. The whole measure is self-defeating.
Anyhow, it’s far from clear that investing in NASA is the best way of going about encouraging space exploration. NASA, for all its good intentions, is a cold-war relic that is just about as effective as any other government agency — that is to say, not very effective at all.
But you know what? I have a distinct feeling this kook won’t get the nomination.