U.S. President Barack Obama speaks to the media after meeting with House Speaker John Boehner at the White House, March 1, 2013 in Washington, DC. (Photo by Mark Wilson/Getty Images) President Obama speaks to the media after meeting with House Speaker John Boehner at the White House, March 1, 2013, in Washington. (Photo by Mark Wilson/Getty Images)

MoveOn.org, the liberal activist group that helped mobilize crucial support for President Obama during his 2008 presidential bid, launched a major effort Wednesday night to defeat the congressional resolution authorizing the use of military force against Syria.

The group, which arose out of Democrats' fierce opposition to the war in Iraq, made its decision after holding a virtual teach-in, monitoring petitions posted on its site and conducting a 24-hour poll that found 73 percent of its members oppose military intervention. Its ability to mobilize the Democratic Party's liberal base could complicate the White House's effort to win some of the House Democrats it needs to pass the resolution next week.

At the same time, Organizing For Action, the non-profit dedicated to galvanizing grassroots support for the president's agenda, has decided to stay neutral on the question of force against Syria.

"We think there's nothing inevitable about this vote, or about this decision," said MoveOn.org's executive director Anna Galland in an interview Thursday, noting the group generated at least 10,000 opposition calls to Capitol Hill on Wednesday night and is helping plan a vigil for Monday night at 7 p.m. local time in communities across the country.

"We are working to channel our members' opposition in a way that will be heard by every single House member and every single senator," she said, noting that CREDO Mobile, the Progressive Change Campaign Committee and other members of the Win Without War Coalition will participate in Monday's vigil.

Given MoveOn.org's previous anti-war efforts, Galland added, it is not surprising they would challenge the administration on this front.

"Our members are quite wary of entering a war, again, halfway across the world in a country that poses no direct threat to our safety and security, and with unknowable consequences in the years to come," she said, noting the fact that some lawmakers have begun discussing the prospect of creating a no-fly zone and providing training to the opposition is particularly alarming. "We're worried about the slippery slope here."

Even as MoveOn.org bombards congressional Democrats about the use of force resolution, one of the president's strongest outside allies, OFA, has decided to stay out of the fight. OFA executive director Jon Carson discussed the issue Tuesday night during a regular call he holds with grassroots supporters; the call was postponed from Monday because of the Labor Day holiday.

"Since the president's announcement on Saturday we've definitely heard from our volunteers on this issue and glad to hear more feedback right now. The first thing I'd say is that it's been pretty universal from folks that they are very glad he is taking this issue to Congress," Carson said, according to a transcript.

"We've certainly heard from all sides of this including people who are just looking for more information on the subject," Carson continued. "What I definitely want you all to know is that OFA supports president Obama and the agenda that Americans voted for on November 6 but we don't always actively organize around every issue, and the debate in Congress over the Syria vote is not one that OFA is planning on organizing around."Carson added that "we encourage people to get more information on this" as the debate moves forward.

Obama's longtime political adviser David Axelrod participated in the Tuesday night OFA call, and Carson then gave him a chance to opine on Syria with the preface, "David you know the president so well, you have seen him work on these really tough issues," but OFA did not release that portion of the transcript.

OFA has been more focused on drumming up support for issues including health care and immigration reform: House Speaker John Boehner's (R-Ohio) spokesman Brendan Buck made a point of noting Thursday that the group is attacking his boss this week, despite the fact that Boehner has endorsed the administration's Syria resolution.

Under the tagline "Makes sense..." Buck e-mailed reporters, "With one of the biggest votes of Mr. Obama’s presidency next week on Syria, OFA is organizing a protest in Speaker Boehner’s district tomorrow on… his opposition to Obamacare."