I quite honestly haven’t seen any sign of that. The existence of crazies on both sides is not proof that crazies are running the show on either side – otherwise they’ve always been running the show. There is, however, some political advantage in throwing bones to the crazies so that they show up to the polls, but that’s also been a feature of democracy since forever.

EDIT: There are clearly Democrats who are fact-resistant – vaccines, cell phone radiation, etc – and I happen to live in a town with more than its fair share of them. But they’re still very much a tiny minority, and safe to ignore. The good and bad thing about Democrats is it’s pretty much impossible to get any reasonably large number of them to agree on anything much more complicated than “water is wet”, and I’m sure you could get some LaRouchites in there to argue that one.