Probably because the NRA is mostly about hunting in PA, less about the more conservative self-defense ethic. But, yeah, that doesn't mean they still shouldn't be able to exert some influence. A lot of those might be in the GOP base already. The suburban, well-off voters are not big on guns or hunting but do cower in fear of global warming. As someone said, those are the counties that turned Dem in the early '90s and the NRA has no influence over them.
But I wasn't thinking about the NRA being able to influence squishy "Republicans" or Green Dems down on the Main Line, so much as helping GOTV and getting the message out that Dems haven't really changed their tune about the 2nd Amendment with those to whom it matters. And they did nothing in the Bush/Kerry election-cycle to counter that moron -- can't remember his name now, used to play for the Redskins -- and his fake "Sensible Gun Rights" PAC that ran so many adds for John "F" Kerry.