Jay Cost has jumped on the polling skeptics bandwagon:

I suspect that when the Democratic enthusiasm bump from the DNC finally settles, we are going to see the two parties sort themselves roughly in line with what they have done through history – meaning a slight edge for the Republicans, not the Democrats. That is also going to shrink Obama’s margin.

Jamelle Bouie responds:

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.

Elsewhere, Bouie and Bob Moser compare Republicans in 2012 to Democrats in 2004:

A cottage industry of liberal bloggers and pundits arose to explain how “biased” sampling had skewed the polls. If you weighted Republicans and Democrats correctly, they argued, then John Kerry would be ahead. But that was missing the point. Pollsters don’t weight the partisanship of the electorate in one way or another. They simply survey a large, randomly selected group of people, and report their party identification. If there are more Republicans than Democrats in a collection of samples, it’s because there are more Republicans than Democrats.

Bush won, as you might recall.

Sam Wang piles on:

I encourage you to focus away from the Presidential race. Of more practical interest are questions where the outcome is uncertain: a few Senate races (ND, IN, MT, and CT), and House control. Karl Rove’s Crossroads GPS is probably making adjustments to reflect this polling reality. It’s hard to imagine them pouring much more money into the Presidential race.