Playing around with the electoral map some more, it seems that it really does come down to Ohio.
The following are considered battleground states:
New Hampshire
Pennsylvania
Ohio
Virginia
North Carolina
Florida
Michigan
Wisconsin
Iowa
Colorado
Nevada
I think it's safe to assume that NC will go to Romney, while PA goes to Obama. Then, while not as safe, let's assume recent trends are accurate and FL goes to Romney, and MI and WI go to Obama. That leaves NH, OH, VA, IA, CO, and NV.
Nevada has a big gun in Harry Reid, and they are becoming more like California, so it probably goes Obama.
Virginia has mostly been with the GOP, apart from 2008. Let's say it goes back to them this year.
That leaves NH, OH, IA, and CO.
In this scenario, Obama would only need Ohio out of those final four to win it, and I think it's unlikely he doesn't carry at least one of the others.