Maine model moves 17 points toward Jackson, to 75 percent

Our model now gives Troy Jackson, the Democrat, a 75 in 100 chance of winning the Maine Senate race against Susan Collins, the Republican incumbent. A week ago, in our run of September 16 at 6:02 PM ET, it gave him 58 percent. That is a move of 17 points toward the Democrat over seven days.

The projected margin moved with it. Our mean margin is now D+4.0, up from D+1.2 in the previous run. The spread of simulated outcomes also narrowed at the edges: our 5th-to-95th percentile range runs from R+5.6 to D+13.5, against R+8.6 to D+11.1 a week ago. Both runs leave outcomes on either side well inside the range.

No new Maine survey is included in the material available for this note. The model moved; what drove it is not something this payload establishes, and we are not going to guess. Shifts of this size in our Maine estimate have come quickly in both directions over the past three weeks, and a 75 percent chance still leaves a Collins win as roughly a one-in-four outcome.

Nationally, our average of 30 generic-ballot polls over the past 45 days stands at D+8.1. Our model gives Democrats a 54 percent chance of winning Senate control, with a mean of 50.7 Democratic seats; Democrats need 51 seats for a majority, Republicans 50, because the vice president is a Republican and a 50-50 tie goes to the Republicans. That arithmetic is why single states like Maine carry as much weight as they do in the Senate picture. In the House, our model gives Democrats a 98 percent chance of a majority, with a mean of 245.3 seats against the 218 needed.