New NY-21 poll shows Republican up 10, and our forecast barely moves

A J.L. Partners survey of 500 likely voters in New York's 21st District, fielded August 15-17, put the Republican at 50 percent and the Democrat at 40 percent.

That is close to what our model already expected. Our forecast now gives the Republican an 84 percent chance in the district and the Democrat a 16 in 100 chance, with a mean margin of R+10.0. The prior run, from 10:30 a.m. ET on Thursday, had the Democrat at 14 percent and a mean margin of R+11.2. The new poll moved the expected margin by a bit more than a point and the win probability by two.

The uncertainty around that central estimate remains wide. Our 5th-to-95th percentile range for the district runs from R+26.8 to D+7.0, which is to say a Democratic win is not excluded by our own numbers, only made unlikely.

Nationally, our generic-ballot average stands at D+6.7 across 25 polls from the past 45 days, and our model gives Democrats a 94 percent chance of reaching the 218 seats needed for House control, with a mean of 242.4 Democratic seats. One caveat on that figure is ours to own: the simulation correlates error nationally, by census division, by state and within each district, but it has no term linking demographically similar districts in different places, because we have no cluster data to build one. That omission makes the House control number marginally firmer than a fuller model would render it.

In the Senate, our model has the two parties close to even, at 51 percent Republican and 49 percent Democratic, with a mean of 50.2 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.