A common theme we keep hearing from conservatives who are unhappy with the public polls is that the surveys assume a 2012 electorate that looks a lot like the one in 2008. For instance, The Weekly Standard’s Jay Cost argues that we should be wary of polls showing a strong national and swing state advantage for President Obama for exactly that reason. It’s worth considering Cost’s argument, because we’ll likely be hearing a lot of this.

Cost wisely stays away from the controversy over partisan weighting; as many pollsters have noted, party identification is a fluid variable that changes with public attitudes. To weigh in one direction or another is to make a particular judgment about how things should look, not how they are. Instead, Cost focuses his attention on two things.

Averaging five polls — Rasmussen, Gallup, Survey USA, Battleground and Pew — Cost finds that Romney and Obama are tied among independents, which for him, doesn’t track with a race where one candidate holds a 4 to 5 point lead over the other. “You do not get a four-point lead overall with a tie among independents, unless you are squeezing substantially more votes out of your base than your opponent is,” Cost writes.

Of course, what could be happening is that more Dem-leaning independents are self-identifying as Democrats than is happening on the GOP side. If so, that would mean the remaining pool of independents could split evenly, even as the overall electorate favors Obama. We don’t know if this is the case, but the point is that there isn’t enough information to make a particular claim about how the race should look based on the independent vote.

Cost raises a second question, and one that’s been echoed by other conservatives — how much will the electorate resemble the one in 2008? Cost is skeptical that Democrats will be as unified and as enthusiastic as they were four years ago. “If it comes down to whether or not this will be a repeat of 2008 — which is basically what the latter camp of pollsters is suggesting — then my money is on no.” He adds later that Obama’s “advantage is built entirely on Democratic enthusiasm, which right now is above its historical trends and clearly on a post-DNC bump.”

This sounds persuasive, until you realize that it’s been nearly three weeks since the Democratic National Convention ended, and there’s no sign of diminished enthusiasm among Democrats. Indeed, despite wide speculation that Obama will have to worry about lower enthusiasm and turnout among core groups — like African Americans and Latinos — the available polling suggests that this is an overblown concern. According to the most recent Pew poll, blacks are as engaged in the election as they were in 2008. Likewise, Public Policy Polling finds that African Americans are the single most excited group in the electorate — with Latinos a close second. Latino Decisions, which publishes a tracking poll of Latino public opinion, also finds high enthusiasm among the group: 46 percent report greater excitement for 2012 than 2008.

Yesterday, Greg interviewed Obama pollster Joel Benenson, who noted the extent to which nonwhites are an increasing share of the vote: “This will be an electorate that has been as diverse as the previous four presidential elections.” Not only is this probably the case, but in all likelihood, these groups will enter November highly energized, and ready to reelect the president.

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