So now we know: The Great Obama Twitter Revolution was an illusion.

At the moment when Obama needs his vast social media army to support him in the debate over health care reform, they are nowhere to be found. No spontaneous meetups. No big Facebook followings. Hardly a tweet on Twitter.

Instead, the dominant images of the health care debate are people shouting down Congressmen at town hall meetings. It’s talk show hosts on cable news channels blustering about the evils of socialized medicine. And it’s radio show hosts pushing the usual propaganda.

Obama has lost control of the debate. And the fight will be soon be lost if the trajectory of the shouting match doesn’t change.

This may be the most critical policy moment of Obama’s presidency. And Obama’s Twitter posse is sitting it out.

What are they waiting for?

Last fall, it was a far different story. All the talk was how Obama’s campaign tapped into the vast wellspring of social media networks to raise unprecedented amounts of campaign funds. They tuned in to the Facebook phenomenon to spread their message, even hiring a former Facebook insider. 

They pioneered the use of Twitter to gain a following in the thousands, back when that was a lot. 

They launched a campaign Web site that allowed users to personalize their pages, discuss and debate policy, and have robust conversations. 

All of this inspired legions of volunteers who took the message offline to begin organizing local meetups. They helped staff phone banks. And when election day came, they helped turn out the vote in a big way for Obama. 

I remember last fall, at the Web 2.0 conference in San Francisco, there was a panel on the future of political campaigns. Howard Dean’s former campaign manager Joe Trippi lauded Obama’s online organizing effort. He said this network of supporters would be felt well beyond the campaign. It would be a powerful tool that could be tapped during important policy moments.

Imagine, when Obama wanted to shape public opinion, he could awaken this network of supporters and call on them to press legislators and the public to support the latest initiative, Trippi said.

Like with health care. Sounds good in theory. But it’s not happening.

It’s hard to explain exactly why the social media army lies dormant. Perhaps health care is just too complex to be debated in a tweet. Perhaps Obama’s plan is too hard to understand. Perhaps it was just more fun, and more clear cut, to organize around a candidate in a campaign, but more difficult to rally people to support a policy proposal.

Whatever the case, the health care issue has not arroused the passions of the social media faithful.

On Joe Trippi’s blog, his subtitle says: “The Revolution Will Not Be Televised.” Perhaps, but the backlash is being televised. And that old fashioned medium has trumped the power of Obama’s Web-based movement.