The answer is yes. If.
If means that just about anything that doesn't violate the laws of physics is possible. Whether it can be done or not depends on how hard and how well people are willing to work for it.
There's a debate going on right now about the precedents for defeating an incumbent. But those precedents don't really matter. If we go by precedents, Obama shouldn't be sitting in the White House at all. The last time a Senator who hadn't been a Vice President or a Governor won an election was JFK in 1961.
