Sen. Olympia Snowe (R-Maine) announced her retirement last month, citing partisanship in Washington, D.C., and now one of the candidates vying to replace her, former Gov. Angus King (I), says he’s not ready to choose a party at all.

With a Thursday deadline for candidates to file in Maine, King’s decision to run for the seat but not divulge with whom he might caucus has thrown another wrinkle of intrigue into the unexpectedly interesting race.

“I have not made up my mind whatsoever. A lot will depend on what the numbers are and depend upon what the actual circumstances are,” King told a Bangor television station over the weekend. “My judgment’s going to be based on what would make me most effective on behalf of Maine.”

It’s unclear whether “circumstances” means the breakdown of individual Senate votes, or the math in the Senate itself, with Republicans hoping to take back the majority and Democrats fighting to retain it. But in a town where everyone has to pick sides, King will eventually have to select a party to caucus with, even if he chooses to maintain his “Independent” label.

There is little precedent for Independent Senators to remain a caucus of one. According to the Senate Historical Office, only one Senator, Dean Barkley of Minnesota, has ever entered the chamber as an Independent and declined to caucus with either party.

Barkley was appointed by then-Gov. Jesse Ventura to replace the late Sen. Paul Wellstone (D) in November 2002, and the Senate was only in session for one week before his term ended on Jan. 3, 2003.

Senators have to choose a caucus if they want seats on committees, which are doled out at the beginning of each Congress by each party’s leadership. In 1952, incumbent Oregon Sen. Wayne Morse left the GOP in protest of Dwight Eisenhower’s selection of Richard Nixon as his running mate.

When the 1952 elections left almost a completely divided Senate, Morse famously put a folding chair in the middle of the Senate’s center aisle as a sign of his independence from Republicans and Democrats. Morse, however, was stripped of his committee assignments and a vote of the full Senate did not restore them. Morse ultimately joined the Democrats at the urging of Sen. Lyndon Johnson (D-Texas), who then became Majority Leader with a one-vote advantage.

In today’s Senate, where a 60-vote filibuster threshold is much more common than the traditional 51-vote majority, there might not be an incentive to stay neutral.

“Something about caucusing that’s important — it’s not only that you don’t get committee assignments, but how often do you take votes with 50-vote thresholds?” asked a Democratic aide. “The notion that you could actually be a tie-breaker on every vote [is out-of-date]. There is every incentive to caucus with one party or another.”

But it’s possible King might have to choose before it gets to that point. Republicans in Maine already have launched attack ads based on his wait-and-see comments, insinuating that King has cut a “backroom deal” with Democrats to try to win back the seat. Before becoming an Independent, King identified as a Democrat.

The last prominent governor to run as an Independent and flirt with caucusing with both parties was Florida’s Charlie Crist, who ended up splitting the vote with former Democrat Rep. Kendrick Meek in 2010.

“No. 1, this is a moot question unless I win, so I’ve got to work very hard to make sure I achieve the trust and support of my fellow Floridians to continue to be a public servant for them,” Crist said in an August 2010 interview with CNN. “I think they know the way I’m going to go. … I don’t have to say whether I’m going to caucus with the Democrats or Republicans.”

Floridians ended up choosing the candidate who said he would caucus with Republicans — Sen. Marco Rubio.

The politics in Maine are somewhat tricky. Snowe and her counterpart, Republican Sen. Susan Collins, built careers on independent voting records, and more than a third of registered Maine voters are independents.

But last cycle, conservative Paul LePage took the governor’s mansion with 38 percent of the vote against a Democrat and an Independent, who received 19 percent and 37 percent, respectively. Fear of a repeat, among other things, led top-tier Democratic candidates such as Rep. Chellie Pingree to decide against running.

Democratic operatives hope that Mainers won’t want to repeat 2010 and would instead lean toward a more independent candidate.

“They’re likely to nominate someone who is conservative, more in line with the national Republican Party, which is going to further isolate them,” said one Democratic operative of the Maine GOP.

As for whether King might split the vote with whoever takes the Democratic nomination, Democrats are keeping their cards close to the vest.

“We’re still waiting to see what the playing field is. There’s what, another two days yet? And we’ll see who files and how it all plays out,” Democratic Senatorial Campaign Committee Chairwoman Patty Murray (Wash.) said.