David Letterman conducted a fairly substantive discussion about the healthcare and automotive industries with Mitt Romney on Tuesday night.

Jay Leno allowed Sarah Palin to whine about being mistreated by the media, and then let her deliver some Alaskan stand-up, as in the temperature is “five degrees below Congress’ approval ratings.” And Palin apparently brought a posse of like-minded fans who whooped and hollered at everything she said.

Unlike other politicians who do latenight talk, though, Palin exhibits no ability to laugh at herself. Even Richard Nixon asked “Sock it to me?” on “Laugh-In.” Palin’s only comfortable when she’s socking it to her perceived enemies.

Letterman still lights up when he gets a politician in the chair opposite him and can discuss issues that go beyond movie promotion. He can still be funny, but in a way that challenges the guest to make and defend key points.

Leno feebly asked Palin about the Tea Party movement but couldn’t muster anything that approached a conversation, except that he liked watching both MSNBC and Fox News so that he was confronted by various points of view. Letterman, by contrast, questioned Romney as to what the Tea Partiers are really angry about, and whether those conditions existed before Barack Obama became president.

Although Palin got to display her TV personality side, Romney came across as a far more serious presidential candidate for 2012. And that was in part because Letterman came across as a host who could step beyond the realm of celebrity blather and actually conduct an interview.

In short, it was a good night for the two people featured on CBS, and despite the whooping and hollering, not such a great one for the two on NBC.