Well, Michele Bachmann has gone already with her paltry 5% showing, so now there are five Republicans left. Obama will face one of them in November, at this stage Romney looks probable (just), although there is plenty of fight left in Gingrich.
From this distance out, I feel Obama will get re-elected. If he wins all the states that John Kerry took in 2004, and retains Florida, he's there.
But a long way to go.