Obama baffles observers, I suspect, because he’s an ideologue and a pragmatist all at once. He’s a doctrinaire liberal who’s always willing to cut a deal and grab for half the loaf. He has the policy preferences of a progressive blogger, but the governing style of a seasoned Beltway wheeler-dealer.
I think Douthat's analysis is pretty dead-on. Obama's liberal instincts for change and social justice are tempered by his deep pragmatism. Evidence of this is not just found in his governance, but in his writing and campaigning. Reading The Audacity of Hope, you get the feeling that his positions aren't seated in any lock-step ideology, but were developed over time, as he explored the intricacies of the issue and applied his education and life experience.
Reading The Audacity to Win, you get a feel for how he balances his desire to be a different kind of politician with his desire to get results. He was reluctant to run negative ads, but he attacked when he had to. He wanted to win, and sometimes that meant slipping back to the old attacks. Through it all, he truly believed in his ability to change America for the better. But he was firmly grounded in reality, rhetoric notwithstanding, and he knew the limitations placed on him.
Liberals may want him to be Dennis Kucinich, but Obama wants to do more than make symbolic gestures, he wants results. How many times have we heard "don't let the perfect be the enemy of the good" from the Obama team? It's not just a strange Voltaire fetish, it's how they believe they need to govern to get results.