From Politico.com:
At high-profile moments, when a large audience is most likely to be watching, Obama usually assumes a deeply earnest tone. And the times do not exactly lend themselves to frivolity.
Obama relies less on actual jokes or clever lines than on good timing and a deadpan sensibility. There is often a post-modern streak to the humor, his lines amounting to self-aware winks at the audience. It is a way of announcing that Obama can simultaneously perform the job of president and offer sly commentary on his own performance.
[Pentagon chief Bob]
A self-effacing punch line is an old standard.
Bill Clinton said something once about how being president is like walking through a graveyard, Kushner noted: You have all these people under you, but no one listens.
When Washington was blanketed in snow a few weeks ago, Obama joked in a meeting that he wanted to go outside and have a snowball fight.
Obama dishes it out in public, too.
The reporters laughed.
Russell said his sense is that Obama will forgo a Washington tradition and not rely much as president on Hollywood-type ghost writers.
The difference between impromptu and planned is usually pretty clear.