In an evenly divided Senate, King could wield significant clout in deciding which party could control the chamber.
That poses a strategic dilemma for the Democratic Senatorial Campaign Committee, which declined to endorse Dill while hoping King, a former Democrat, would eventually line up with Senate Democrats.
Only recently, after King's slide in the polls, the DSSC began airing more than $400,000 in TV ads accusing Summers of "marching with Washington extremists."
King's independence could create an opening for Republicans who hope to capitalize on King and Dill splitting Democratic and independent votes to pave the way for a Summers win.
Dill, 47, said she's heard plenty of voters fret that her candidacy could tip the race to Summers, but she'll keep fighting because no one else is standing up for her progressive values.
King's lead over Summers has fallen from 30 percentage points in June to 22 points, a recent poll published by the Maine Sunday Telegram showed. King led Summers 50-28 percent while Dill had 12 percent.
King has hit back with an ad accusing Summers of favoring subsidies for big oil and a pledge against new taxes that King says makes it impossible to solve the deficit.
Maine has a long tradition of independents: Republican Sen. Margaret Chase Smith, often split with her party during her four terms before losing in 1972. And during Watergate, Maine Republican William Cohen broke ranks as a congressman and voted to impeach former President Richard Nixon. Cohen later became defense secretary in the Clinton administration.
"Maine's an independent state that votes the person, not the party," said Laura Garland, a 37-year old bartender and waitress from Bangor who is a Democrat backing King and Obama.
Jeff Jones, 42, a supervisor at Bath Iron Works, is a Republican who plans to vote for King and Republican presidential candidate Mitt Romney.
Jones and Garland said they're not bothered by King's refusal to wear a party label.
"You vote for a man's integrity," said Jones. "I like Angus."
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