I thought about that in the past. Initially I thought the same. I still think it's possible. But I also remember thinking the same thing during the Bush vs Kerry campaign. In the end, the day after the election was quiet - just another day. I got the feeling that the Kerry loss was not so drastic to the dems after all. I suppose it could work out the same with Obama. Just a guess.
There would be two exceptions:
1) If the election results are too close.
or
2) Obama refuses to concede (even after an obvious defeat) and somehow tries to stay in power.
Then things could get violent.
The difference with the “Bush-Kerry” event was that Kerry (to his credit) didn’t spend four years stirring up the masses and encouraging a race-war if he didn’t get his way. Obama is not only inept but dangerous - he would rather see this country go down than suffer the humiliation of a loss.