Well it depends. The current Republicans tend to want someone slightly right of Khamenei. If they put forth a candidate like that, then Obama will win easily. Really, the easiest way to win right now would be to put forth a candidate that actually leans left instead of someone who has a few left views but overall is right of center like Obama. Obama is beginning to show that he's not liberal enough to really fix this country the way it needs to be. And unfortunately the current conservatives have proven that anyone who falls even right of center they think of as a socialist.
I think Obama still has a chance. Unfortunately this oil spill fiasco came at a bad time. And the president cannot fix everything. He was spending so much time fixing the economic problems Bush caused, that he didn't fix the oversight problems Bush caused. And then there's the problems trying to fix Afghanistan which wouldn't exist had Bush handled that anything but ineptly. If the current republicans would actually work with Obama and stop trying their hardest to be complete obstructionists then shit would get fixed. But they don't want shit fixed, they want as many problems as possible so they can blame Obama. Then they'll aim to usher in a massive shift right so they can set up the American version of Iran as a Christian run totalitarian nation with a figure head president that is actually run by high cleric Rush Limbaugh.