Se. Patrick Leahy (D-Vt.), center, speaks to the media after attending a closed meeting for members of Congress on the situation in Syria on Sunday. (Joshua Roberts/Reuters)

The White House is preparing to mobilize the full power of the bully pulpit to push members of Congress to approve attacks on Syria, even as the administration refuses to say whether or not they would proceed with strikes against Bashar al-Assad’s forces if the vote doesn’t go their way. “The strategy will be to flood the zone … everything is on the menu,” an unnamed official told Politico.

The vote will be unlike any other of the Obama era in that there is no clear partisan position and deep divisions on both sides. Much has been made of the split on the right between hawkish neocons and isolationish libertarians, but the left has its own divisions here as well.

While liberals are almost universally supportive of President Obama’s decision Saturday to seek the approval of Congress, BuzzFeed’s Evan McMorris-Santoro reports that they’re divided on what Congress should actually do. Democracy for America, the grassroots organizing group that grew out of the Howard Dean presidential campaign, sent a remarkable e-mail to its members explaining why the group is refraining from taking a position:

“Thoughts are still coming in, but after our team reviewed responses from over 40,000 DFA members…only one thing was clear,” reads the email from Jim Dean, Howard’s brother and DFA’s chair. “We are not united as a community. And if we tried to call for one united action in response, we’d be dividing our members — instead of uniting behind them.”

Adam Green, the co-founder of the Progressive Change Campaign Committee told McMorris-Santoro his group was still “getting [our] head around it all,” pointing to a New Yorker article by George Packer titled “Two Minds On Syria,” that captures the liberal ambivalence about a possible attack.

The truth is, this division is nothing new on the left, but was obscured by the near-unanimity against the Iraq war. But with a Democrat in the White House, things are much more complicated.

Private conversations with progressive activists and operatives reveal liberals are pulled between three desires: 1) There are the “liberal interventionists,” who want to strengthen international human rights and non-proliferation norms and try to stop the suffering; 2) There’s an anti-war camp, which wants to avoid another violent foreign entanglement; and 3) There’s a desire from some to support the president, who has staked his reputation at home and abroad on a vote to authorize the use of force.

Remember, it was liberals (including some in Obama’s Cabinet) who spearheaded the humanitarian military interventions of the 1990s, and sought to strengthen the international human rights regime with tools like the “Responsibility to Protect,” which creates a legal requirement for countries to use force to stop war crimes. And in the mid-2000s, it was largely liberals who pushed the Bush administration to intervene in Darfur, Sudan, especially the type of young, educated, tech-savvy, progressives who would later form the volunteer base of the Obama campaign.

Rep. Eliot Engel, the top Democrat on the House Foreign Affairs Committee, echoed this human rights-first sentiment after a classified briefing with administration officials Sunday. “If we stand idly … it will send a message to every despot across the world and every terrorist group across the world that you can commit war crimes and there’s no penalty for it,” he told Politico.

Mia Farrow, the liberal actress and activist whose son served in Hillary Clinton’s State Department, has been preaching intervention daily to her 125,000 Twitter followers. After Obama announced Saturday that he’d wait for congressional approval, she remarked:

Meanwhile, groups like MoveOn, which fought the Iraq war, have been vocally opposed to intervention. Some even told the Huffington Post’s Ryan Grim that Democratic leaders in Congress, including liberal icon Nancy Pelosi, should be replaced if they support the war effort. “It’s time to change the House leadership,” said Howie Klein of Blue America.

Inside Congress, that sentiment bubbles up to people like Sen. Patrick Leahy (D-Vt.), the most senior Democrat in the Senate, who told reporters that the resolution seeking military force from the White House was is “too open ended.” He said top Senate aides are currently drafting new language with more restrictions.

Meanwhile, both sides are aware that if the White House loses the authorization vote in Congress, it could weaken the president and thus make it harder for him to push other progressive agenda items and draw a hard line with Republicans in upcoming fiscal battles. Indeed, White House aides were shocked when Obama decided Friday night to seek congressional approval, we learn today from the Wall Street Journal’s Carol Lee.

This split has been present since the beginning of the Syria conflict. “We are of two minds, as a group, about this,” Democratic Rep. Keith Ellison, who chairs the House Progressive Caucus, told me over a year ago. “One is human rights: When I went and got arrested in front of the Sudanese Embassy [protesting the genocide in Darfur]… it was progressives who were standing there next to me getting arrested, too.”

“On the other hand… our military engagements in the past has been sullied by questions like this, to the point where many progressives just don’t even believe it if the U.S. government says we’re there for humanitarian reasons,” he added.

But now that military intervention is an immediate possibility, and members of Congress will have to go on the record with their votes, liberals need to speak up, one way or the other.