The percentages involved with "swinging" the popular vote are small but super important. There is no need for a popular tidal wave of support.
I agree with eskimospy. Also, you can't place a value on the fact that the GOP, for the Presidential election of 2012, can NOT claim Obama will be soft on terror and terror sponsoring countries.
The GOP lost almost half of the election playbook when Obama got OBL.
One issue is, though, that Obama is going to face corporate funding like never before.
Even if the right loses, history shows that the most trivial of issues can have big influences on elections, used in powerful marketing campaigns (and media collusion).
Remember how the guy who had the best bit of political credit in years - Al Gore's role in leading the funding for creation of the internet - was turned into a negative for him.
The GOP may have lost some lines of attack against the terrorist loving commie Kenyan, but the money spent attacking him for *anything* might matter more.
IMO, Obama has a good chance to win - with a big wildcard being the economy that Republicans seem bent on making as bad as possible to help them win the presidency - because of the advantages of incumbency and how bad the Republicans are as well as some nice wins like the auto industry bailout over the Republicans' objection and defending Medicare - but these big budget ad campaigns can outweigh the facts.
For example, remember right-wingers arguing for how the first Bush 'deserved' to beat Clinton because of his war record over Clinton's 'draft dodging' - and yet reversed themselves to turn John Kerry's war record into a negative for him (swift boat liars) compared to draft-dodging George W. Bush.
It's a bit ironic that IMO the killing of bin Laden shouldn't be a big campaign issue for anyone who did it, but it actually helps Obama counter some of the marketing.
What idiocy we have when our election campaigns are swayed by things from insane slogans ('he pals around with terrorists') to a mission that has little to do with his real qualifications for running foreign policy. The lesson being taught here seems to be to tell every president to make sure they find an enemy they can use for building support, that they can kill a bit before the election. Worked for Bush with Saddam, too.