The South Dakota numbers were not bad for Mr. Obama — putting him down by 6 points, closer than the margin by which he lost the state in 2008 — but look like something of a fluke. In North Dakota, which has been more heavily polled because of the competitive Senate race there, Mr. Obama has consistently trailed by double digits.

Indeed, with the presidential election likely to be much closer than it was in 2008, Mr. Obama is unlikely to paint any new state blue this year. The forecast model gives him a 15 percent chance of carrying Montana, which has been sparsely polled; a 14 percent chance of winning Missouri; and an 8 percent chance of winning Arizona.