But the convention narrative revolves around her in important ways.

It's not just because so much drama attaches to the question of how she and embittered husband Bill regard Obama, and not just because she and Bill are getting so much air time. Obama has two major challenges this week - and both are Hillary-centric.

First, Obama has to win over Hillary's voters from the primaries, only 52 percent of whom are now supporting him, according to the latest Wall Street Journal/NBC News poll.

Second, he has to occupy the space on the political spectrum that Hillary carved out in the primaries - identifying himself with mainstream American values, demonstrating a toughness on foreign affairs and connecting with the working class with his economic policies. (If he's at a loss how to do any of it, perhaps Hillary can explain it over a shot and beer chaser.)

That Obama is still performing so poorly among Hillary voters makes the prominence he's given the Clintons look less like an abject capitulation and more like a strategic necessity. If the Clintons can deliver Hillary's voters, every minute devoted to them will have been worth it.

The Clintons, of course, are profoundly conflicted. They've long thought Obama will lose, but they can't betray that belief lest - should Obama actually fail in the fall - they get blamed, engendering the bitterness of half the party.

Yet, no matter how enthusiastic they are (or seem), there's only so much the Clintons can do to deliver Hillary's voters. Some of these people are simply angry that she lost, and can be placated by seeing her treated well. But others were attracted by her characteristics - that she was tougher and more experienced than Obama. That group will be harder to reach.

Obama's pick of Joe Biden as his running mate is an attempt to play for these voters. Problem is, Biden's experience isn't transferable. It doesn't matter that Biden has spent 35 years in the Senate; Obama still has spent less than four.

The Georgia crisis helped tip Obama toward foreign-policy maven Biden as his VP choice. But, as Saturday's rally rolling out the ticket showed, Biden's value is as much his working-class roots as his work on arms control or Iraq (most of which has been terribly misconceived).

Obama portrayed Biden as a politician who came from the working class and never left it - the champion of, as Mark Penn put it in one of his campaign memos for Hillary, the "invisible Americans." Here, too, Biden's utility is probably limited. Most voters will look at him and not see the scrappy kid from Scranton, Pa., but a senator whose love affair with hearing himself talk is ardent even by the self-exalting standards of the breed.

So neither the Clintons nor Biden will be able to make the sale for Obama: He'll have to make it himself - and the convention is one of his best chances to do it.

He'll need to express sympathy with the morés of the middle of the country and blunt the sharp edges of his party's social liberalism, something Clinton did during the primaries in emphasizing her Midwestern roots and with her caution when addressing hot-button social issues. He'll have to sound tougher on foreign affairs, something Hillary did with some well-placed bluster about "obliterating" Iran.

And he'll have to make the connection between his domestic policies - from taxes to health care to energy policy - and the interests of the middle class, a centerpiece of Hillary's campaign.

Assailing John McCain, which will be a favored sport here, doesn't substitute for any of this. In the end, the election is essentially about Obama, and whether he can connect with average voters and meet the standard of commander-in-chief. And the way Obama should go about it is all about Hillary.