DENVER - It has become a tradition at national conventions to speculate on the size of the presidential candidate's "bounce."
The gold standard was set by Bill Clinton in 1992, when the newly anointed Democratic nominee busted out of his convention and rolled by bus across the swing-state heartland, buoyed by a hike of 16 percentage points in the Gallup poll.
So naturally, everybody wonders how big Obama's bounce will be. Surely he's going to surf a big wave in the wake of his unified convention, right?
The fact is, Obama will barely see any upward bounce.
Yet, as the pollsters tell me, this has nothing to do with Obama or his convention.
It has everything to do with the unique logistics of this particular convention season.
Start with the fact that the Republicans are staging their quadrennial meeting right after the Democrats break camp, with only a holiday weekend in between.
This makes it impossible for the pollsters to take any meaningful readings.
Indeed, several big polling operations are not even bothering to survey at all during the Labor Day holiday weekend.
The Republicans know all this, of course, but they would never say so publicly.
Quite the contrary, their current strategy is to pre-spin the expectations game by contending that Obama should be deemed a flop if he fails to bounce like Bill Clinton did, or like Jimmy Carter did in 1976 (nine points up), or Ronald Reagan did in 1980 (eight), or George W. Bush did in 2000 (eight again).
Hence, the McCain campaign memo last week, which purported to predict: "Obama will see a significant bump, and [we] believe it is reasonable to expect nearly a 15-point bounce out of a convention in this political environment."
Those who are obsessed with the notion of a post-convention "bounce" - the partisans angling to win, the journalists seeking an angle - seem to forget something important.
It's called history.
Some of the biggest bouncers wound up losing: Al Gore in 2000 (eight-point bounce), President Carter in 1980 (10 points), Mike Dukakis in 1988 (seven).
And some of the smaller bouncers wound up winning: Richard Nixon in 1968 (five), and President Bush in 2004 (two).
Besides, the TV audience for national conventions has been steadily shrinking, which suggests that their impact on the national mood is waning.
So skip all the chatter about an Obama bounce out of Denver, or a McCain bounce out of Minneapolis, and just check back with the polls in mid-September.
By that point, any lingering convention story lines and impressions will be factored into the national mood.