Democrats at 96 in 100 for the House, 47 percent in the Senate

Our model, updated at 6:32 AM ET on September 17, gives Democrats a 96 percent chance of winning a House majority and Republicans 3 percent. The mean Democratic seat total is 242.3, against the 218 needed for control. Our House simulation draws correlated error at four levels — national, census division, state and district — but has no term linking demographically similar districts in different places, because we have no cluster data for it. That omission makes our House control number marginally firmer than a fuller error model would leave it; we have not measured the size of the difference and are not adjusting for it.

The Senate is close to even. Our model gives Democrats a 47 in 100 chance of a majority and Republicans 53 percent, with a mean of 50.0 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 the Republicans.

Our generic ballot average stands at D+7.2, drawn from 27 polls fielded over the past 45 days. Recent surveys span a wide range. Big Data Poll, sponsored by the Public Polling Project and fielded September 13-15, had Democrats ahead 50.5 to 39.3 among 2,633 likely voters and 47.8 to 38.1 among 2,947 registered voters. Beacon Research and Shaw & Company Research, for Fox News, had Democrats ahead 51 to 44 among 1,211 registered voters, fielded September 11-14. YouGov, for the Economist, put the margin at 51-39 among 1,051 likely voters and 44-39 among 1,455 registered voters over the same dates. Ipsos, for Reuters, had 44-37 among 896 registered voters and 39-31 among 1,143 adults.

The largest move on our board was Ohio, where the Democratic win probability rose 34.1 points to 72 percent. North Carolina moved up 7.9 points to 84 percent and South Carolina up 7.0 points to 13 percent. Minnesota moved down 27.1 points to 68 percent and Maine down 24.4 points to 58 percent; Iowa moved up 11.5 points to 42 percent. Our Minnesota and Maine estimates have since settled a few points above where they stood yesterday.

The underlying state polling is tight in three of those races. In Minnesota, co/efficient found the Democrat at 43 and the Republican at 42 among 833 likely voters on September 14-15, with 2 percent for an independent and 2 percent for others; SurveyUSA, for KSTP-TV Minneapolis, had the two tied at 42 among 654 likely voters fielded September 9-14. In Maine, Quantus Insights put Susan Collins at 47.6 and Troy Jackson at 47.4 among 621 likely voters on September 14-15, a race too close to separate. In Iowa, co/efficient had Ashley Hinson at 46 and Josh Turek at 42 among 831 likely voters fielded September 14-16. Wedgewood Polls had Pete Ricketts at 52 and the Democrat at 48 in Nebraska, among 500 likely voters over the same three days.