I may have been rather critical of President Obama's rather uninspiring (for him) acceptance speech at the Democratic National Convention, but was rather more impressed by his performance on the David Letterman Show the other night, prompting as it did an interruptive burst of applause (scroll in 40 seconds) -- just after he'd used a nice simple contrast:
"My expectation is that, if you want to be president, you got to work for everyone, not just for some, [APPLAUSE STARTS] "and the uh--"[APPLAUSE CONTINUES]
As noted elsewhere on this blog (and in my books), the contrast is one of the most important rhetorical devices for triggering applause in political speeches. And, as is evident from this example, it can work in the same way in other settings too (e.g. TV interviews).