Impact Research poll of MT-1 leaves our forecast where it was

An Impact Research survey of 500 likely voters in Montana's 1st District, fielded September 20-23, found Democrat Sam Forstag at 47 percent and Republican Aaron Flint at 44 percent. Nick Sheedy, running outside the two major parties, drew 2 percent. With a sample that size, the race reads as close rather than as a clear edge for either candidate.

The poll did not move our forecast. Our model gives Forstag a 60 in 100 chance of winning the seat, the same as in the run completed earlier this morning. Our projected margin stays at D+2.1. The only change is at the edge of the range: the 5th-to-95th percentile band now runs from R+12.1 to D+16.3, against R+12.2 to D+16.3 before.

The new survey largely confirms what was already in our average. Its three-point gap sits close to our model's mean margin, so it added little new information. The Democrat's chance was 59% when we last wrote about this race on September 28, and it now stands at 60%.

The width of that range is the more useful number. With 34 days to the election, our model still treats outcomes from a double-digit Republican win to a double-digit Democratic win as plausible.

Nationally, our model puts the Democrats' chance of winning a House majority at 98%, with an average of 245.2 Democratic seats against the 218 needed. That figure is somewhat firmer than it should be. Our simulation correlates error nationally, by census division, by state and by district, but it does not link demographically similar districts in different places, because we lack the data to do so.