NYT/Siena has Pappas up five in New Hampshire, and our forecast holds at 87

A New York Times/Siena University survey of 613 likely voters in New Hampshire, fielded September 15-22, put Democrat Chris Pappas at 49.8% and the Republican at 44.8%, a five-point gap.

Our forecast did not move. We give Pappas an 87 in 100 chance of winning the open New Hampshire Senate seat, with a mean margin of D+11.6 and a 5th-to-95th-percentile range running from R+5.2 to D+28.5. That is identical to our previous run, completed at 4:32 AM ET on September 24. The new poll is narrower than our central estimate but comfortably inside that range, so it confirms rather than changes what the model already had. Our published number for this race was 85 on September 18; it is 87 now.

The race matters to the chamber arithmetic. Our model has the Senate split almost exactly down the middle: a 50% chance Democrats win control against 49% for Republicans, with a mean of 50.4 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. A seat our model treats as 87% Democratic is not what is driving that coin-flip, but it is part of the base it is built on.

The national picture is steadier. Our generic-ballot average stands at D+8.1 across 30 polls in a 45-day window, and our House model gives Democrats a 98 in 100 chance of a majority, with a mean of 245.3 seats against the 218 needed. One caveat on that House figure is ours to own: our simulation correlates error nationally, by census division, by state and by district, but we have no data to correlate demographically similar districts across state lines. Without that term, the 98% is marginally firmer than a fuller model would make it.