The Maine Peoples' Resource Center Public Opinion Survey still gives King a substantial lead over his opponents, with 44 percent support to Summers's 28 percent support, and Dill receiving only 15 percent support. But in the last poll from MPRC, in early April of this year, before campaigning had started in earnest, King drew 56 percent of the vote.

That shrinking lead could be because King is making gains with everyone but Republicans. With that group, he lost 14 percent support, 8 percent of which went to Summers, who made gains with all party affiliations since the start of the campaign.

A poll from Democratic firm Public Policy Polling gives King a far smaller lead, pegging him at 43 percent support to Summers's 35 percent and Dill's 14 percent support.

And his popularity in the state has dropped drastically since the start of the campaign, according to the PPP poll. Now only 52 percent of voters have a favorable opinion of him, from 62 percent in March — and the amount of Maine voters rating him unfavorably jumped 11 percentage points since then.

The PPP polling memo points out that King is having trouble convincing Republican voters to back him, with only 13 percent support from that group, and is still losing more than a quarter of Democratic voters to Dill. The memo speculates that King, who is eventually expected to caucus with Democrats if he wins, may have to more explicitly come out with the party to receive its backing.

The MPRC poll was conducted among 856 registered Maine voters in likely voter households from Sept. 15-17, and has a margin of error of 3.35 percent.

The PPP poll was conducted among 804 likely Maine voters from Sept. 17-18 and has a margin of error of 3.5 percent.