But when Obama let Biden take over the cliff talks, and when he noted with asperity that he would not debate Congress again over paying its bills, he dug into his revulsion at playing the game, his reluctance to even fake the flattering, schmoozing and ring-kissing needed to coax Congress into doing what he wants.

Even members of his own party have lost faith in his ability to use the White House as a social lubricant to get his agenda passed, or to use that big brain of his to become a more clever negotiator, rather than a scolding lecturer.

"His inability to engage the politicians here has been a real liability," one Democratic lawmaker complained. It's odd, given that he was renowned for making a group of egotists feel that they were being heeded at The Harvard Law Review.

The vice president was in the Senate for 36 years while the president merely breezed through. Obama radiates contempt at Congress for not being a bunch of high-minded, effective people, and for expecting him to clean up its mess. He thinks reasonable people should see things his way in a reasonable amount of time, and gets impatient when ideology, ego, identity politics and pork-project whining hold up progress.

Biden is a realist. He understands lawmakers' limitations, motivations and needs. He leans right in and speaks — and speaks and speaks — their language. That's who he is. And he believes, as creaky and unwieldy as the system is, that it still has integrity. More Rocky than Spocky, Biden can spread everything out on the table and negotiate his way through all of his former colleagues' shortcomings, weaknesses, fears and frailties.

It's actually fun for him, while Obama seems so often to be pulling back, aggrieved by the need to engage. The president and his staff seem clueless about what Republicans on the Hill are thinking. And Obama ignores those who urge him to be less insular and — like Jefferson, Lincoln, L.B.J. and Reagan — socialize more with political players, combining fairy dust, elbow grease, intimidation and seduction to get his way.

Joe Biden has a valuable skill: He knows how to stoop to conquer.