I don't know that it's so simple. Dems don't generally prioritize gun anything much. It's not a cornerstone of their platform. They'll talk a bit about 'well we need reform here and there' and that will dip into things like 'assault weapons ban' and whatever else, but for the most part it's not an issue they're talking about all the time to begin with.

That doesn't stop the perception being that they are the 'anti-gun party' from existing though. I mean, you needn't look further than Obama himself. He's talked about some of the problems, he's implored us all to consider things, that we can be better. But he ultimately has barely done anything pro or against 'guns' from an executive position. Didn't stop the image of him being the most anti-gun, coming to get your guns, better stock up while you still can, from proliferating far and wide.

The Right is good at working a fervor, particularly when there's little to get worked up about. "If you're not explicitly for" turns into "You must be 100% against and actively trying to enforce your views!". And people eat that shit up, as evidenced by the recent election.