In the lead-up to the war in Iraq in 2003, more than 100,000 protesters in New York jammed the streets near the United Nations building, where, less than two weeks earlier, then-Secretary of State Colin Powell made the case that Iraqi officials were "concealing their efforts to produce more weapons of mass destruction."

On Thursday, a few hundred protesters stood in Times Square to voice their opposition to U.S. military action against Syria. There were no celebrity appearances as in 2003, when Archbishop Desmond Tutu, Susan Sarandon, and Danny Glover gave speeches in the February cold.

In Britain, the discrepancy is similar. Organizers in London say 1,000 people gathered outside of 10 Downing Street on Wednesday night to protest a proposed strike on Syria, with 5,000 expected to attend Saturday. A decade ago, anti-war activists claim two million people marched through the streets of London to protest the war in Iraq, the largest demonstration in the city's history.

Both conflicts involved a regime accused of harboring "weapons of mass destruction." So why does anti-war sentiment from the left seem so much more tepid this time around?

"One obvious theory is that Syria is just vastly different from Iraq — no one's talking about sending in ground troops this time," writes The Washington Post's Brad Plumer. "That could explain why the opposition isn't quite so fierce."

So far, U.S. military intervention looks like it would be limited to cruise missile strikes from American warships and possibly air strikes launched out of Turkey, although those would be considerably more risky considering Syria's highly capable, Russian-made air defense system. Regardless, a lengthy occupation to "win hearts and minds" looks unlikely.

In Iraq, the submitted evidence of WMD was abstract, and ultimately erroneous. Now, in the age of social media, YouTube is filled with reported evidence of the regime of Syrian President Bashar al-Assad launching chemical weapons attacks against civilians, including heartbreaking images of children's corpses shrouded in white cloth.

"You can argue that Assad's use of chemical weapons is a bad reason to attack, but it's harder to argue that the Obama administration is simply inventing a reason to invade a country it has been wanting to invade for years," writes Slate's Joshua Keating.

Of course, things could change. Protests could grow if the U.S. acts unilaterally or gets mired in a longer conflict.

But it might not be the actual conflict that is holding protesters back — it could be the man in the Oval Office.

"The Democrats are missing in action because of course the president is a Democrat," David Swanson, an anti-war activist working with non-profit group Roots Action, told BuzzFeed. "What's tamping down the activism is partisanship."

Plumer points to a study by sociologists Michael T. Heaney and Fabio Rojas, who claim that participation in anti-war rallies plummeted significantly after 2008, despite the fact that Obama has continued some of the national security policies implemented by George W. Bush, and for a while even ramped up the U.S.'s military presence in Afghanistan.

Part of the reason, the study says, is that Democratic politicians in the Bush era found it politically useful to co-opt the anti-war movement for votes. That all changed after Obama was elected:

The rise of Democratic majorities in Congress and a Democratic president in the White House presented opportunities for activists to press their cause, but this possibility was precluded by the removal of a critical causal mechanism: perceived threat (from President George W. Bush and the Republican Party). [PDF]

Ultimately, the study suggests, the anti-war rallies of 2003 weren't just about Iraq — they were also a way to register disapproval with the Bush administration. Now, even with most Americans wary of military intervention in Syria, the Democrats who marched a decade ago are mostly staying home.

Or, as former Rep. Dennis Kucinich (D-Ohio) told BuzzFeed when asked about the state of the left, "What anti-war movement?"