If Barack Obama wants to get a serious bounce in the polls from his speech tonight, the gifted speaker should eat some humble pie and copy dull old Al Gore.

At the 2000 Democratic Convention, Gore gave one of the best acceptance speeches in recent history. And by "best" we mean a 17-point bounce in the polls.

Until he spoke, the then-vice president had endured three bad convention nights and netted no upward bounce. His running mate's speech, given by rhetorically challenged Joe Lieberman, had fallen flat, while Hillary and Bill Clinton stole the show.

But Gore's speech brought him from a seven-point deficit to a 10-point lead.

By Election Day, of course, the race had tightened into a nail-biter, largely because Gore blew the debates. But he gave himself a better send off coming out of his convention than any recent candidate.

But what can Obama learn from Gore? Well, Gore basically gave a State of the Union speech - at the risk of boring the audience, he laid out to TV viewers a complete presidential program, delving into each area of substance and articulating his plans in detail and with specificity.

The media highlighted his prolonged kiss with Tipper on the stage as the reason for his bounce, but it was really a speech bursting with specifics that gave him his edge.

Voters have been very impressed by Obama's opening act. His charisma, intellect and message have thrilled tens of millions, especially among the young. But, so far, he's had no second act - he's been unable to follow up the generalities with specifics or to put flesh on the skeletal message of change.

Now, in his acceptance speech, the nominee needs to go where he hasn't been before and answer the implicit question voters always ask of candidates who run on promises of change: Where's the beef?

Obama has chosen a hard venue for such a serious message. Performing in a stadium crammed with 75,000 adoring fans is a task more suitable to a quarterback than a candidate for president.

The temptation will be to engage the crowd, playing off its energy and creating a scene of unparalleled enthusiasm and energy. Obama will want to go into his revivalist speaking style replete with choruses of "yes we can" and "not this time." He'll want to reprise the best of his primary-night victory speeches and his Berlin address to create an explosion of support, an outpouring of adulation.

Such a scene will make great TV and will likely even give him a good bounce - but the glow will dissipate quickly. Americans have seen this act before; on reflection, they want more steak and less sizzle.

With John McCain's vice-presidential announcement following hot on the heels of Obama's speech and the Republican convention coming to order just 72 hours later, Obama's bounce from an "empty" speech won't last; he'll be lucky to end up in a tie coming out of the conventions.

But a substantive speech setting out a program will strike just the right chord with voters and will give him the same kind of bounce that sustained Gore in 2000 (and kept Bill Clinton's ratings aloft for eight years).

Obama hasn't had a bad convention so far - because he hasn't had any convention. It's as if the gathering in the Pepsi Center belongs to the Clintons - and he has to leave for the expanses of Invesco Field to have his convention.

In fact, the Democratic nominee not only has realized no bounce from the proceedings so far, he may actually be the first candidate to lose ground during his own convention.

He needs a home run tonight, not just a blast from the revivalist past. That means he needs to give us an Act Two of substance.