^ that's always the case. If it worked everytime we wouldn't have revolutions or secessions anywhere in the world. Keep in mind that the army is composed of people who get paid, who have fears and desires, who will be uncomfortable fighting their own etc.
OT - Not yet I think, but personally - as I've already said - the things on the USA seem to be going that way. I don't think reelecting Obama is going to be enough to trigger anything close to a civil war. Such extreme events need a bit more fuel than that. It needs a final sledgehammer, such as a very bad economic collapse, and then a single, isolated event to trigger it.
Right now, despite the reports of recovery some might have been misled to believe, the economy has never been that bad. The money simply isn't flowing anymore:
What is holding the american economy on its feet? Maybe the same reason Japan hasn't collapsed yet: floating debt and rampant speculation... I don't know, take your picks. But the situation is that of a house of cards. A single blow to its fragile structure and it could collapse. A hyperinflation could very well start in some months. Who knows.
The rest, as they say, is the unthinkable. History is filled with stuff that never would happen.
Would a civil war succeed? I think so. China and Russia, besides using the opportunity to seize Belarus, Taiwan etc., are probably going to support the rebel cause. An United States divided in two, three nations at attrition among themselves are much less of a world power.