Another close South Dakota poll, and our numbers do not move

A Public Policy Polling survey of 629 registered voters in South Dakota, fielded September 8-9, had Republican incumbent Mike Rounds at 45 percent and independent Brian Bengs at 42 percent. The poll does not report a margin of error, and a three-point gap in a sample that size is close.

Our forecast did not change. The model gives Rounds a 99 percent chance of winning the seat, with 1 percent for another candidate and no measurable Democratic path, since no Democrat is on our ballot for this race. The mean margin is R+24.0, unchanged from our previous run at 6:32 a.m. ET on September 11. The 5th-to-95th percentile range moved from R+41.8-to-R+6.1 to R+41.9-to-R+6.1, which is noise rather than news.

That is the whole of it. This site has already written twice about South Dakota polling that pulled our margin around without touching the odds; this time the poll did not move the margin either. The gap between what the survey shows and what our model shows is large, and the model is weighting this one poll against everything else it knows about the state.

Nationally, our average on the generic ballot is D+6.7 across 24 polls over the past 45 days, as of 8:02 a.m. ET on September 11. For Senate control, our model gives Democrats a 48 in 100 chance and Republicans 51 percent, with a mean of 50.2 Democratic seats. Democrats need 51 seats for control and Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to the Republicans. South Dakota is not among the seats that decide that.