In a move that could complicate the Democratic Party’s efforts to hold the Senate, Dem Rep. Chellie Pingree — a favorite of national liberals and progressives — has decided not to run for the seat of retiring Olympia Snowe, a Democrat familiar with her thinking tells me.

The decision will disappoint national liberal groups who had mounted a campaign to draft her for the race. Pingree is seen by liberals as an unabashed defender of progressive principles — she has been an aggressive advocate for the public option and for marriage equality, and has crusaded against corporate money in politics. Installing her in Snowe’s seat would have been a major coup for the left, which is perpetually looking for progressive voices to counterbalance “moderate” Dems that are often too politically skittish to embrace the liberal/Dem agenda.

But Pingree, after looking closely at her chances, determined that entering the race could pose too great a risk to Dem chances of holding the Senate, the Democrat familiar with her thinking tells me. Pingree did see a path to winning, and passing on the race cut against her competitive nature. But the entry of independent former governor Angus King would have meant they’d compete for many of the same voters, making a Republican victory more likely — a risk she was not prepared to take, the Democrat says.

“From the data we’e seen, there is a big correlation between people who are likely to support Angus King and her base of support,” the Democrat says. A Public Policy Polling survey found that King would beat Pingree and Republican Charlie Summers in a three way race, and notably, 51 percent of King’s supporters would want him to caucus with Dems, versus only 25 percent who would want him to caucus with the GOP.

“They tend to attract the same kind of voters,” the Dem says. “Making Mitch McConnell the majority leader could have an impact on which Supreme Court nominees could get confirmed. This was not something she was willing to put her personal ambition ahead of.”

National Dems wanted Pingree to run. They had seen Snowe’s retirement as a huge pickup opportunity and even a safeguard against losing control of the Senate. The path forward is now unclear.


UPDATE: The NRSC, in a statement, insists that national Dems may not have wanted Pingree to run and is hoping to get King to caucus with Dems:

Pingree’s decision should come as no surprise given the fact that since Senator Snowe made her announcement a week ago, there has been absolutely no effort by national Democrats to recruit or gather signatures for any viable Democratic candidate, including Pingree, ahead of next week’s March 15th filing deadline.

UPDATE II: The Progressive Change Campaign Committee, one of the leading groups behind the draft-Pingree momement, responds:

“Chellie Pingree would have been a bold progressive fighter in the Senate, and we are confident that she will be when Susan Collins retires. Angus King was willing to create a three-way race that handed this Senate seat to a far-right Republican — a precise repeat of what happened in Maine’s 2010 three-way gubernatorial race. Chellie Pingree’s decision was based on what is best for the people of Maine and the future of progressive causes, not based on what was best for herself, and we look forward to continuing our work with her around progressive fights in Congress.”