The historical trend I

[nclib]

Only two presidents won re-election with a lower EV-percentage than in their 1st election, that were James Madison in 1812 and Woodrow Wilson in 1916. So it looks like this happens every hundred years ...

That said, I wouldn't be surprised if Obama wins by a lower margin (EV or PV) than in 2008. Obama benefitted from W. Bush's unpopularity that year. If it was Obama vs. McCain in a neutral political climate, Obama would probably still have won, but by a lower margin than in real life.