Obama simply has to choose the less worse option - war or breaking an alliance. Either one is a risk to his election but looking at the Republicans, he's looking pretty comfortable.
I think the US will probably offer some limited military support but nothing major.
I don't know, it could be pretty close - Romney will likely be the Republican candidate and we've seen his ability to wage a massively negative campaign with pots of cash. If the economy goes back down and the negative publicity is strong enough, it could go back to the Dark Side.