Maine model moves 25 points toward Collins, to 61 percent for Jackson

Our model now gives Democrat Troy Jackson a 61 in 100 chance of winning the Maine Senate race against Republican incumbent Susan Collins. A week ago, in our run of September 3, it gave him 87 percent. That is a move of 25.5 points of win probability toward Collins over seven days, the largest single-week shift we have recorded in this race.

The expected margin moved with it. Our model put the mean outcome at D+7.0 last week and puts it at D+1.7 now, with a 5th-to-95th-percentile range of R+8.4 to D+11.8. The comparable range a week ago ran from R+3.4 to D+17.4, so the downside has deepened and the upside has come in.

Three surveys of the race are in the payload. A CNN/SSRS poll of 880 likely voters, fielded August 31 to September 6, had Jackson at 48 percent and Collins at 45. YouGov, fielding September 2 to 8, had Jackson at 48 and Collins at 44 among 1,335 likely voters, and Jackson at 46 and Collins at 44 among 1,378 registered voters. None of the three reports a margin of error in the payload, and all three are close. We wrote about the CNN survey when it landed; the YouGov pair is what is new since.

Those numbers are consistent with a tight race, but they do not by themselves account for a 25-point swing in probability. The model moved further than the polling in front of us plainly explains, and we are not going to assign a cause we cannot document. Nationally, our model gives Democrats a 39 percent chance of Senate control, with a mean of 49.6 Democratic seats against the 51 they would need; Republicans need 50, because a 50-50 tie goes to them on the vice president's vote.