While it's commonly accepted that Angus King, a former Democrat who supports President Barack Obama, would align with Democrats, he has refused to say. That's generated suspense and, in theory, could translate to power for King if the Senate ends up close to a 50/50 split. If one party wins a decisive majority, King could find himself with less leverage than he hoped.
"It looks like the Democrats may hold the control of the Senate -- I'm not ready to concede that, but they may -- in which case there ain't going to be no negotiating," said former Senate Majority Leader Trent Lott, R-Miss. "He'll go to the Democratic side and take what they give him."
Who wields power after Tuesday's election is all about the math, but the answers may not be immediately clear.
If President Barack Obama wins re-election, he needs 50 Democrats or Democratic-aligned independents to keep control of the Senate. And similarly, Mitt Romney would need 50 Republicans or independents who lean that way if he wins.
If one party wins the White House and the opposite party wins the Senate, it'll take 51 votes. That's because the vice president has a tie-breaking vote. There's a chance that uncalled races for Senate seats in states like Montana or Wisconsin, or even an uncalled race for the White House, could mean that control of the Senate might not be known on Election Night or even for days afterward.
So what happens if it turns out that King is the deciding vote?
"I'll see what's going on when I get down there and what's best for Maine and the country," he said when asked about his party affiliation during a campaign stop last month in Bath, Maine.
Favored in the race to replace retiring Sen. Olympia Snowe, one of the GOP's most prominent centrists, King has made his independence the core of his campaign. He's such a household name in Maine that his campaign yard signs -- "Angus, independent for U.S. Senate" -- don't even give his last name.
He tells voters his independence could translate into clout.
In an evenly divided Senate, King could wield that power from the start over the question of which party could control the chamber. As a former popular two-term governor, longtime TV show host and former Senate aide, King is a big personality who seems to relish the prospect of such a role.
In theory, King could use his leverage to win favorable committee assignments or promises of debate on pet legislation.
But in the waning days of the campaign, Democrats are increasingly favored to maintain control of the Senate -- with or without King. He may not have the leverage he hopes.
Former Majority Leader Tom Daschle, D-S.D., says King's clout may depend on how narrow control of the Senate is.
"The closer you are to 50/50, the more leverage you have. The less close you are, your leverage starts to dissipate," Daschle said. "But a leader needs every vote he can get in the Senate these days, so there's always leverage."
King insisted he's made no deals with party leaders on either side. He has said he could align himself either with Democrats or Republicans, and has even suggested he could switch from one to the other, depending on the issue.
"There's some value in being uncommitted and having people have to court you a little bit," he said.
Despite King's talk, national Democrats are betting he will side with them more often than with Republicans. The Democratic Senatorial Campaign Committee has declined to endorse the Democratic nominee in the race, Cynthia Dill. And the DSSC has run ads against King's Republican rival, Charlie Summers.
The GOP seems to assume King will line up with Senate Democrats. The National Republican Senatorial Committee and GOP-leaning outside groups have spent millions of dollars on ads against King.
King has urged voters to elect an independent voice to help break Washington's partisan gridlock, saying it could spark other states to follow suit.
He's a former Democrat who backs Obama, but who also supported George W. Bush in 2000. He supports Obama's health care overhaul. His views on issues like abortion rights and environmental causes track most closely with Democrats.
During his campaign, King cited his record for cutting taxes, making targeted infrastructure investments, bolstering the state's rainy day fund, setting aside land for conservation and winning high marks for Maine's bond rating.
King has some familiarity with Capitol Hill, too. He was an aide to former Sen. William Hathaway, D-Maine, in the 1970s. He returned to Maine to practice law in 1975 and began an 18-year stint as host of the "Maine Watch" television show.
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