Springfield too close to call. But I bet Capital City tends Democrat.
Also, there are other elements to consider. Springfield has a fundamentalist school, and despite Reverend Lovejoy's idea of a good church service, there seem to be a lot of churchgoers, particularly given that there are several other churches. So this suggests that the Ned Flanders factor may be rather hefty in Springfield. This suggests that there's a hefty Further, I think Krusty is explicitly a Republican in one episode (as is Dr. Hibbert, but they got him right). Springfield also used to have a nearby military base, but as it has since closed, there might not be any lingering after-effects. But Birch Barlow, a Rush Limbaugh figure, apparently has a very large audience in Springfield; and Rainier Wolfcastle would, no doubt, be a major fundraising force for the Republicans. Carl and Lenny, though, are certainly Democrats (Carl admires Ted Kennedy for his integrity, for instance).
This all reminds me of my two favorite Simpsons politics one-liners:
No children have ever meddled with the Republican Party and lived to tell about it. - Sideshow Bob
Oh my God...the dead have risen and they're voting Republican. - Bart
Both of these, of course, are from the Sideshow Bob Roberts episode.