Senate near a coin flip as our House estimate holds at 96 percent

Forty-eight days out, our model gives Democrats a 48 in 100 chance of winning a Senate majority and Republicans a 52 percent chance. The mean outcome in our simulations is 50.1 Democratic seats. Democrats need 51 seats for control; Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to them. That single-seat asymmetry is most of why a forecast whose central estimate rounds to 50 seats still leans Republican.

In the House, our model gives Democrats a 96 percent chance of a majority and Republicans 4 percent, with a mean of 241.4 Democratic seats against the 218 needed for control. One caveat belongs to us rather than to the data: our simulation draws correlated error nationally, by census division, by state and by district, but has no term linking demographically similar districts in different places, because we lack the cluster data to build one. Without it, our House control number is marginally firmer than a fuller accounting would leave it. How much firmer is not measured in this run.

Our generic ballot average stands at D+7.0, drawn from 25 polls over the past 45 days. The recent readings are wide. A Morning Consult survey of 30,013 registered voters, fielded September 7-13, had Democrats ahead 46.3 to 42.4. The New York Times/Siena University poll of 1,503 likely voters, fielded September 8-13, had it 51.28 to 42.76, and 49.01 to 42.18 among registered voters in the same sample. An Economist/YouGov poll fielded September 11-14 had Democrats up 51 to 39 among 1,051 likely voters and 44 to 39 among 1,455 registered voters. A Reuters/Ipsos survey fielded over the same dates had Democrats at 44 to 37 among 896 registered voters, and 39 to 31 among 1,143 adults.

The largest forecast change of the past week was in the Ohio Senate race, where our estimate of the Democratic chance rose 18.4 points, from 39 percent to 57 percent. Maine moved the other way, down 16.5 points to 75 percent. Iowa rose 12.2 points to 44 percent and North Carolina rose 8.2 points to 83 percent. Minnesota fell 14.6 points to 80 percent.

Nebraska produced two new numbers. A SurveyUSA poll for Grant Forbes, LLC, fielded September 8-13 among 503 likely voters, put the Democrat at 46 percent and Republican Pete Ricketts at 42. The same sponsor's survey of 182 likely voters in NE-2 had Denise Powell at 46 and Brinker Harding at 42, a close result on a small sample. In Texas, a SoCal Strategies poll of 649 likely voters fielded September 12-13 had James Talarico at 50 percent and Ken Paxton at 45. Our estimate there is now 70 percent, up 9.4 points on the week.