UNH puts Pappas at 50 in New Hampshire, and our forecast stays at 87

A University of New Hampshire poll of 1,392 likely voters, fielded September 17-21, has Democrat Chris Pappas at 50 percent and the Republican at 42, with 2 percent for another candidate.

Our model gives Pappas an 87 in 100 chance of winning the seat, and Republican Scott Brown a 13 percent chance. Those are the same numbers our previous run produced earlier on September 24. The mean projected margin moved from D+11.8 to D+11.7, and the 5th-to-95th percentile range is now R+5.2 to D+28.6, against R+5.0 to D+28.6 before. This is a poll that confirmed the existing average rather than reset it.

The UNH result sits slightly above our mean margin but well inside that range, which still includes outcomes where Brown wins by several points. Neither candidate is an incumbent; the seat is open, and the current occupant is Democrat Jeanne Shaheen.

New Hampshire matters to our Senate picture because the chamber is close to even. Our model gives Democrats a 52 percent chance of winning Senate control and Republicans 47 percent, with a mean of 50.5 Democratic seats. Democrats need 51 seats for control and Republicans 50, because the vice president is a Republican and a 50-50 tie goes to the Republicans. A race we score at 87 percent is therefore part of the assumed base, not the source of the uncertainty.

The national backdrop is a generic-ballot average of D+8.3 across 30 polls over the past 45 days. In the House, our model gives Democrats a 98 percent chance of winning a majority, with a mean of 245.7 seats against the 218 needed. One caveat on that figure is ours: 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, so the House number is marginally firmer than a fuller model's would be.