Experience

In his Time Magazine article Does Experience Matter in a President?, David von Drehle makes an excellent point:

Presidential experience means a familiarity with the levers and dials of government, knowing how to cajole the Congress, understanding when to rely on the Joint Chiefs of Staff and when to call on the National Security Council — that sort of thing. But bear down even slightly, and the notion of experience is liable to crack and run all over. If knowing the system is so useful, then second-term presidencies should be more successful than first-term. Instead, many Presidents lose effectiveness as they go along.

Great point in general, but particularly in an Obama v. McCain race. Why? Because the first reason one would give for declining effectiveness in second terms would be general fatigue. And would, say, a 50-year-old second termer likely be more fatigued than a 72 -year-old first termer?