No snark: it is a man-killing job, Democratic or Republican. My rule of thumb is that being President effectively ages you 2.5 years for every one, and with Obama it’s showing.
Not to give the President any unsolicited advice or anything, but: more basketball, less golf. Seriously. George W. Bush did a lot of running to keep the stress down and the heart-rate up; I don’t know if basketball is worse, better, or as good as an alternative to running, but it’s got to be better cardio than golf is.