How often does either party primary an incumbent president? Wikipedia only lists five notable one. And also has this little factoid that shows it usually backfires for the party.
Since the advent of the modern primary election system in 1972, an incumbent president has never been defeated by a primary challenger, though every president who faced a strong primary challenge went on to be defeated in the general election.
Edit - Forgot my wiki link. =(
Well like I've said in one of these threads, it really was the perfect storm for him. That was about as bad as he has looked and sounded in his almost 4 year term. I saw video of him at a campaign stop the next day and it was like night and day. He was still old, and still had a cold, but he looked more alive - for lack of a better word.
But I 100% agree that the party's only choice shouldn't be a rich white senior citizen. The minimum age requirement is 35, and we should be shooting for closer to that, rather than well past "retirement age".