Some cents from Friendly Sword;
To preface, I'm a leftist from a mysterious foreign country who dislikes Obama.
That being said, my wager would 7-1 for Obama assuming that Romney takes the nomination. If any of the outfielders get it, say Gingrich, Santorum, Paul, then my bet would be more like 20-1.
Why? Three big reasons.
#1- 'Centrist' American voters tend to hate change, and for Presidential elections especially, there is a pattern of centrists swings to the incumbent nearly every election. Statistically the incumbency advantage is huge and bipartisan in nature. Look at how few President's have been one-term Presidents. It has generally required a combination of a poor economy, extreme personal weaknesses, and a dynamic opponent. While Obama certainly has the first, I'd say he isn't facing the same kind of opposition that, for example, Jimmy did.
#2- The Federal Republican Party is still wandering in the wilderness. Don't get me wrong, America is still a helluva Conservative Party and in both Congress and most states the Republicans are either in control or could be in a few years. No, it is specifically the federal Republican party that has gotten hijacked by it's lazy but effective propagandizing. At a certain point, the spin got out of control, and until Republicans can succeed in the primaries without being a) crazy like Bachmann or b) sane like Romney but momentarily pretending to be crazy they will be hampered either by their disconnect with wider American society or their hypocrisy. I say this, because there is absolutely no way any of the Republican candidates can win the federal election with the rhetoric they use in the primaries. This problem exists in the Democratic Party too, but the Republicans have it waaaaaay worse, and until it is rectified, they will be hard to win in 2016, much less 2012.
#3- Obama isn't a failure, he isn't a Marxist, and he isn't even much of a Leftist. Most attacks against Obama fall into two paradoxical categories. Either he's a radical with an insidious agenda, or he's an incompetent buffoon who doesn't deserve to be in office. The contradictory nature of these criticisms belies a boring truth. Obama doesn't really believe in advancing progressivism (at least the politician Obama doesn't) and hasn't been that successful in pushing leftist agenda's. You could argue that he's been moderately successful in increasing Executive power (ordering drone strikes, directly controlling stimulus) but I wouldn't say that increased executive power n there ways is either a leftist or a rightist project. Otherwise though, he's been competent at doing what American Presidents are expected to do these days; the economy isn't great but hasn't collapsed perhaps in part due to his management, he has avoided personal scandals, and he's aggressively pursued American foreign policy interests, threatened fake enemies, exercised muscles etc. In reality, he's little different from Bush, and like Bush, I think he'll get re-elected.
But what do I know.... my country just elected a robot to a majority government last year... maybe American's will do the same. :D