Remember Nixon in 1972 and Clinton in 1996. An unscrupulous President can do a lot of things to screw up the other party's nominating process, and the Chicago machine around Obama will probably make CREEP look like a Sunday school picnic when it comes to dirty tricks and illegal behavior. All Obama has to do to be re-elected is to make sure the Republicans don't nominate someone with widespread appeal.
You mean like a quirky third party candidate and a Bob Dole?