Democrats received a rare opportunity to take back a Senate seat in Maine from GOP hands when Sen. Olympia Snowe announced last week her retirement.

But that has changed now that Angus King, an independent and popular former governor, is expected to announce Monday evening his campaign for a seat held by the Republican moderate since 1994, The Portland Press Herald reported.

King, who served two terms as Maine's governor from 1995 to 2003, declined to confirm his plans, but rejected the idea he would siphon off votes in a race whose outcome is critical for the two major parties duking it out for control of the Senate.

I don't go into campaigns planning to be a spoiler, King told the Press Herald. When I go into a campaign I go in planning to win.

With Maine being friendly terrain for Democrats, the party was primed to take the seat now that the popular Snowe is leaving the Senate. An independent candidate complicates their efforts by giving the GOP a path to victory.

There had been another independent candidate mulling a Senate campaign -- Eliot Cutler, a lawyer who placed second in Maine's 2010 gubernatorial contest -- but he declined to make the race.

Cutler Monday gave his support to King, should he pull the trigger on a Senate bid.

I hope that he will run, Cutler wrote to supporters on his Facebook page. He would bring to the Senate the independence, the abilities, the reputation and the disposition that will make him a great senator, that will serve us Mainers well and make us proud every day, and that will begin to rebuild and restore the Senate to what it was intended to be, the world's greatest deliberative body.

The deteriorating reputation of an increasingly partisan Senate was one of the factors that led Snowe to drop her re-election plans.

In The Washington Post, Snowe wrote that the Senate is not living up to its billing by failing to adopt a budget, political brinkmanship and competing, up-or-down, take-it-or-leave-it proposals.

As for candidates running under a party banner, U.S. Rep. Chellie Pingree and former Gov. John Baldacci are leading Democratic candidates; for Republicans, Maine Attorney General Bill Schneider, Treasurer Bruce Poliquin and former lawmaker Rick Bennett will run, according to the Press Herald.