While President Barack Obama has struggled to keep the center together, he’s had one unquestioned political success: Keeping the left at bay. A battle-tested Democratic infrastructure fell into line behind the White House, with regular meetings and conference calls to coordinate strategy and preempt any breach of message discipline – easy on the Tim Geithner! – or what chief of staff Rahm Emanuel might regard as obstructionist behavior.

That alliance, which endured in spite of sometimes emotional differences on the shape of health care legislation, is now under increasing strain. Obama’s commitment of 30,000 troops to Afghanistan Tuesday night has energized a left increasingly angry at what it perceives as Obama’s accommodations with the center and an energized right.

MoveOn is one of the handful of groups breaking from the White House’s hold on big liberals to raise money, activate volunteers and threaten for the first time, Obama’s left flank. And so is a pixie-ish 50 year old former Hollywood producer who named her blog after her dog, and is taking what she calls “the next step in our evolution.”

The campaign launched by Jane Hamsher, whose blog Firedoglake first came to national attention for obsessive coverage of the Valerie Plame investigation, is called, “One Voice for Choice,” and uses the nifty online phone banking tools that helped power Obama’s campaign to put a scare into House Democrats who voted to attach the anti-abortion Stupak Amendment to health care legislation.

The calls will target, in particular, pro-choice Democrats in those typically conservative district, threatening to cut the base out from under Democrats who are straining to reach out to the other side.

“We’re taking something that was like gold to them and that they were counting on having and saying they can’t take it for granted,” she said, describing House Democrats’ tendency to take the progressive base for granted.