Why the generic ballot might underestimate Democrats

Still, the notion that specific Democratic candidates do slightly better than generic ones would square with what we’re seeing elsewhere in the data. It also arguably squares with the respective strategies of the two parties, as Republicans are generally trying to nationalize the race, while Democrats — lacking much in the way of a coherent national message — are trying to localize it. Mr. Arcuri, for instance, the Democratic incumbent we discussed above, did not vote for the Democrats’ health care bill the second time it came up for a vote in the House (although he did vote for it the first time), which might immunize him from some “generic” Republican attacks on “Obamacare.”

None of this is likely to save Democrats from having a rather poor November. But, it could make the difference between their losing around 55 seats in the House, which is about what you get if you look at the generic ballot and ignore all other indicators, or more like 40, which is about what you get when you look solely at local indicators and ignore the generic ballot. Our forecasting model, which looks at some combination of the two, now pegs’ Democratic losses at around 45 seats but with a large amount of uncertainty on either side of that estimate.