I generally see the definition of "bemused" to be synonymous with "confused" or "puzzled", and that it is wrong to use it as a synonym of "amused". However I tend to see it used — as Obama did today — as sort of a mixture of "puzzled" and "amused." Like when you shake your head and chuckle at people who get hung up over a silly issue. Which is how Obama seemed to be using it, and how I would tend to use the word myself. After all, there isn't another word that captures that meaning.
Am I correct in this interpretation? Is the meaning of the word subtly changing over time, possibly because it sounds sort of like "amused"?