(a) Obama leads Obama voters only 84-13. Now, some 2008 McCain voters have died or won’t vote for Romney; some 2012 Obama voters will be new voters; some 2012 Obama voters will be 2008 McCain voters; that 84-13 may well turn into 90-10 on election day. But it’s hard to see where the improvement in D turnout is going to come from when so many Obama voters are disaffected.

(b) Independents overwhelmingly favor Romney, by 20 points in some polls. It’s implausible that independents have swung so wildly, yet Democrats are more enthused and more likely to turn out than Republicans. Some, such as Josh Marshall, have posited that the makeup of independents has been changed because disaffected Perot/Tea-Party/Paulite conservatives have left the Republican party. Dan McLaughlin’s counter-argument strikes me as stronger. Even under Josh Marshall’s calculation of voter ID, D+7 among “all adults” should not translate into a 2012 that is better than 2008 for Democrats: Republicans are more likely to vote; Republicans are more likely to vote for Romney than Democrats for Obama (especially given the shift in Catholic opinion since 2008); and Marshall necessarily concedes that the independent vote will be less pro-Obama than in 2008. And I don’t believe Josh Marshall that the current makeup of all adults is D+7…

(d) Some polls show Republicans more excited about this election than Democrats; others show the excitement level about even. But even taking the latter polls as an accurate metric, the relevant comparison is again versus 2008, where the Democrats had a huge excitement advantage. If the Democrats are going to outperform 2008, which they have to achieve the slim lead they achieved in 2008 given the shift in independents, they need to be more relatively excited than in 2008. They’re not.

(e) The Obama campaign is assuming turnout will be 72% white; polls are assuming turnout will be 74% white. But there’s a strong argument that turnout will be more like 75% white. Whites favor Romney by about 61-39; non-whites Obama about 80-20. This would be a shift of 0.8% relative to the polls.