Angus King, the independent senator-elect from Maine, hasn’t decided with which party he plans to caucus next year, and doesn’t rule out joining with Republicans despite the party’s decision to spend millions of dollars in attack ads against him.

King, a popular former two-term governor who served as an independent from 1995 to 2003, will succeed Sen. Olympia Snowe (R-Maine) next year after winning election Tuesday night with 53 percent of the vote. Snowe’s surprise decision to retire instead of run for reelection spoiled the GOP’s hopes of regaining the Senate majority, especially once King jumped into the race and cleared the field of any significant opposition.

As for the possibility of joining with Republicans, King said in an interview Thursday, “I’m not ruling it out, I’m not ruling it in. I’m not ruling it out with the Democrats one way or the other either.”

“I hope to be able to make a decision next week and move on,” he added. “There’s no reason to drag this out. I’m not being coy, I’m not trying to draw attention to myself, I just want to do something that’s true to what I committed to my constituents up here and that is to be a good senator on their behalf.”

King’s decision to caucus with Republicans would serve as a serious embarrassment for Senate Majority Leader Harry M. Reid (D-Nev.) and Democrats, who declined to support members of their own party in Maine’s Senate race on the assumption that King would join them next year. If King joins with Democrats, the party would enjoy a 55-seat majority, just five votes short of the 60 votes needed to break filibusters.

King said he plans to meet with party leaders next week on the sidelines of new member orientation. His decision will be based on two criteria: “One that will allow me maximum of independence and one that will maximize my effectiveness.”

“I’ve had people urge me and not really talk to either side and not take a committee assignment and plant the flag in the middle of the aisle,” King said. “But I’m not inclined to do that because it makes what I’m doing a stunt. And it’s not a stunt, I have a commitment to the people of Maine to get things done on behalf of the state.”

He declined to say which committees he hopes to join, saying he would only disclose his preferences during those private meetings next week.

In a sign of how important his decision could be in advancing the Obama administration’s priorities in the next four years, King said he’s already heard from President Obama and Vice President Biden, who both offered congratulations, but didn’t ask about his decision.

“It was all about working together for the country, which is a pretty good idea, I think,” he said.

A senior administration official said the White House wouldn’t confirm with which incoming lawmakers Obama has spoken, but said he spoke with several Thursday.

King said he also heard from Reid, who encouraged him to speak with Joseph I. Lieberman (Conn.) and Bernie Sanders (Vt.), two independent senators who have caucused with Democrats: “That’s as far as he went in an argument or in making the case, just to say that ‘We’ve worked with two other independent senators.'”

An aide to Reid confirmed that the leader had spoken with King and the senator-elect’s characterization of the call.

Among Republicans, he said he’s heard from Snowe and Sen. Susan Collins (R-Maine) as well as Sens. Roy Blunt (R-Mo.) and Bob Corker (R-Tenn.). Notably absent from his list of calls is Senate Minority Leader Mitch McConnell (R-Ky.), whose aides didn’t return requests for comment.

Several observers — none of whom are directly familiar with King’s thinking — have surmised that King is unlikely to join with Republicans because the party and several conservative super PACS, including the U.S. Chamber of Commerce, spent millions of dollars in attack ads in hopes of bolstering GOP candidate Charlie Summers.

But King said those ads won’t factor into his ultimate decision.

“That’s history. And I didn’t like it, and I didn’t think it was productive and I didn’t think it was true or fair, but one thing I’ve learned in politics is that yesterday’s enemy can be tomorrow’s ally depending on the circumstances,” he said. “Obviously I’m human and I can’t ignore what went on, but it’s not a deciding factor.”

King and other new members of the House and Senate will arrive in Washington next week amid a new eagerness for both sides to work together. House Republicans are sounding a more conciliatory tone, pledging compromise and cooperation in the face of GOP losses, and McConnell has also signaled he’s willing to work with Obama if the president begins shifting toward the political middle. King said that the new tone bodes well for progress.

“The fact that the president is now in his final term – there’s no more motivation to make him look bad or have him cooperate or not have him have successes, I think that removes a motivation to partisanship,” he said. “There’s no reason to try to frustrate or deny him what might otherwise appear to be a legislative success, because he can’t run again anyway.”

He recalled meeting a voter recently who told him, “All my life, I’ve wanted a chance to vote for none of the above, and you’re it.”

“I think that really sort of sums it up,” King said. “I think the political system, the parties need to realize that people are going to be looking for ways to vote for none of the above unless they begin to solve these problems in a cooperative fashion.”

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