Speaking on Good Morning America today, White House senior advisor David Plouffe said he doesn’t expect a substantial bounce for President Obama following the convention:

“This is a very tight race,” Plouffe said. “We’ve always believed that there’s very little elasticity in the election. I don’t think you should expect a big bounce. I think this is a race where we’ve got a small but important lead in some battleground states. It’s going to be very, very close all the way out.”

Obviously, Plouffe is playing the expectations game — it’s always better to be surprised with more support than you were expecting than to be chastened by less than you predicted. Still, there’s plenty of evidence for Plouffe’s skepticism. Conventions are rarely a place where parties convince voters to join them, rather, they give a reason for disaffected supporters or partisan “leaners” to support the party. You saw this last week with the Republican National Convention; Romney didn’t bring voters to his side as much as he unified his support among Republicans.

If Obama receives a bounce, it will almost certainly be for the same reason. Remember, there are remarkably few undecided voters this year — Gallup’s tracking poll shows the number of undecideds at around 8 percent, and in a survey released this summer, the Pew Research Center put the percentage of undecideds at five percent. In all likelihood, any additional support he receives will come from Democrats — and Democratic-leaning independents — who are reminded of why they supported Obama in 2008.

With that said, I think there’s a small chance of a more significant bounce. The Romney campaign assumes that there is a group of voters who need permission to vote against a president they like and admire but who has failed. But there’s a chance that this goes both ways. These voters — or at least some of them—are also looking for a reason to support Obama despite their disappointment with him, because they like him and want to see him succeed. Taken as a whole, the Democratic National Convention has amounted to a sustained pitch to these voters, made explicit by Bill Clinton’s declaration: “No president — no president, not me, not any of my predecessors, no one could have fully repaired all the damage that he found in just four years.”

If this message sticks, and voters feel that Obama is moving in the right direction and has a plan to get the economy on track, then he could walk away from this convention with a larger-than-expected bounce, and a solid position for the final stretch of the campaign.

Jamelle Bouie is a staff writer at The American Prospect. You can find his blog here.