McCain will win over Obama by a modest margin (5%) or so. He'll beat the war drums, and lavishly point out the Democrats are coming to tax your wealth away. Too many Americans will resonate with these points, resulting in a simple-majority win for McCain.
About 2 years into his term, McCain will pitch over in a heart attack or something, and his Veep (Romney, most likely) will become Prez. Naturally, the Iran War that McCain started in 2009 will just continue, and 5000 US soldiers will die in the Iranian fields in 2009 alone.
By 2010, there just won't be a news outlet that won't be using the term "Depression" to describe what's going on in the USA. Martial-law like crackdowns will happen monthly in certain US cities, to combat riots over a lack of food and gasoline.
By 2012, there's going to be a serious movement in the Congress to put aside the Presidential election to let Commander-in-Chief Romney "handle the domestic emergency".