Unless a gun control debate erupts over it (which hasn't happened yet, so it probably won't) this isn't the sort of thing that affects a presidential race.
It did affect 2000, though. Gore's pro-gun control stance helped him immensely in the suburbs, and that was mostly a result of Columbine.
Gun control certainly did affect the race in 2000. It also screwed him over in a lot of areas - there were a lot of rural areas out West where Clinton did well, Gore did awfully, and then Bush's standing fell between 2000 and 2004.
It's an ever-present "cultural" issue, but I don't see these shootings having anywhere near the effect of a Columbine.
Then again, I was 10 in 2000, so I should probably stfu.
