A single Ohio poll leaves OH-15 close and our forecast nearly unchanged

A Hart Research survey of 401 likely voters in Ohio's 15th District, fielded August 6-9, put the Republican at 41 percent and the Democrat at 37 percent. On a sample that size, a four-point gap does not establish a lead. The race is close, and a sizable share of respondents picked neither candidate.

Our model now gives the Democrat a 35 in 100 chance in OH-15, with the Republican at 65 percent. The mean margin is R+4.1. Our 5th-to-95th percentile range runs from R+21.2 to D+13.2, which is wide enough to include comfortable wins for either party.

That is close to where the forecast already stood. Our previous run, at 2:30 p.m. ET on August 17, had the Democrat at 37 percent and a mean margin of R+3.8. The new poll moved the estimate by about two points of win probability and three tenths of a point of margin. It confirmed the prior reading rather than changing it.

Nationally, our average of 26 generic-ballot polls over the past 45 days stands at D+6.7. Our model gives Democrats a 93 percent chance of winning a House majority, with a mean of 242.1 seats against the 218 needed. One caveat on that figure is ours: the simulation correlates error nationally, by census division, by state and within each district, but it does not include a term linking demographically similar districts in different places, because we have no cluster data for it. That absence makes the House control number marginally firmer than a fuller model would produce.

In the Senate, our model gives Democrats a 45 percent chance of control, with a mean of 50.0 seats. Democrats need 51; Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to them.