InsiderAdvantage poll finds a close Maine Senate race; forecast barely moves

A new InsiderAdvantage survey of 1,200 likely voters in Maine, fielded September 22-23, finds a close Senate race. It puts Democrat Troy Jackson at 46.4 percent and Republican Sen. Susan Collins, the incumbent, at 45.6 percent. A gap that small is not a lead.

The poll confirmed what our model already showed. Our forecast now gives Jackson a 61 in 100 chance of winning, down from 62 percent in the run earlier today. Collins's chance rose to 39 percent from 38 percent. Our model's average margin held at D+1.7.

The range of outcomes in our model remains wide. Its 5th-to-95th percentile runs from R+7.8 to D+11.1, nearly unchanged from R+7.7 to D+11.1 in the previous run. Both a comfortable Collins win and a comfortable Jackson win sit inside that band, and the new poll did nothing to narrow it.

Maine matters to the national picture. Our model gives Democrats a 56 percent chance of winning Senate control and Republicans a 44 percent chance. Democrats need 51 seats for a majority; Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to them. Our model's average outcome is 50.8 Democratic seats, just short of the Democratic threshold.