Maine Democratic Reps. Chellie Pingree and Mike Michaud have begun the process of building Senate campaigns, even though neither has come to a final decision on whether to run to succeed retiring Sen. Olympia Snowe (R).

Sources in both camps maintain that the looming March 15 deadline to file forced the two Representatives to move ahead with gathering petition signatures as they still mull a Senate run.

While there have been reports that national Democrats are pushing for the two Members to decide between themselves which of them will run for Senate, it is not beyond the realm of possibility that the two will square off in the Democratic primary, according to a Maine Democrat.

Adding to the chaos, former Gov. Angus King (I) told Roll Call this morning that he is “actively considering” a run for the Snowe seat. In recent history, Maine has elected independent candidates statewide.

Republican names in the mix include  former gubernatorial candidate and Ambassador Peter Cianchette; ex-state House GOP Leader Josh Tardy; University of Maine Athletic Director Steve Abbott; state Treasurer Bruce Poliquin; and state Attorney General Bill Schneider. Scott D’Amboise was a long-shot candidate already running for the GOP nomination.

With the Senate field very much still in flux just 24 hours after Snowe’s surprise announcement, Roll Call is changing the rating of the race from Safe Republican to Tossup. Democrats should have the edge in the open-seat contest in a presidential year, but the possibility of a three-way race featuring a well-known Independent and the potential for a major Democratic primary battle are big unknowns.

If one or both of the Democratic Members run, it will set off a domino effect for politicians interested in lining up to run for the state’s two House seats. Sources in both parties say they have ready benches.

Pingree’s 1st district is heavily Democratic and should be easier for Democrats to hold in the event it becomes an open seat. But Michaud’s 2nd district is much more competitive and was already expected to feature a closely watched House race. State Senate President Kevin Raye (R) had launched a serious challenge to Michaud, and Democrats and Republicans agree that if Michaud runs for Senate, GOP chances of winning the seat will greatly improve.

That said, Raye has also been batted around as a potential Senate candidate.