Markey leads by 19 in new UNH poll; our forecast still gives him the seat

A University of New Hampshire survey of 881 likely voters in Massachusetts, fielded August 20-24, put Democratic incumbent Ed Markey at 49 percent and Republican John Deaton at 30 percent. That is a 19-point lead, with about a fifth of the sample not landing on either candidate.

Our model's read on who wins did not change. It gives Markey a 100 in 100 chance, the same as in the run dated August 26 at 10:30 PM ET. What moved is the expected size of the win. Our projected margin is now D+27.4, down from D+32.6 in the previous run, and our 5th-to-95th percentile range has shifted to D+16.5 to D+38.1 from D+21.8 to D+43.5.

So the new number is confirmation on the question of the outcome and a small correction on the question of scale. Our average still sits well to the right of what the poll shows on margin, which is why a survey with a 19-point Democratic lead pulls the projection down rather than up.

The national picture behind this race is closer. Our generic-ballot average, drawn from 24 polls over a 45-day window, is D+6.6. In the Senate, our model gives Democrats a 44 percent chance of winning control and Republicans 56 percent, with a mean of 49.9 Democratic seats. Democrats need 51 seats for a majority and Republicans need 50, because the vice president is a Republican and a 50-50 tie goes their way. On that arithmetic, a race our model treats as settled contributes nothing to the uncertainty; the chamber turns on the seats where the projected margin is a fraction of D+27.4.