In the wake of President Obama's deal to extend the Bush tax cuts to the wealthiest Americans, pundits have focused on how Obama has alienated the left. But the issue isn't the left - it's the list.

Obama entered the White House with more than a landslide victory over Sen. John McCain. He brought with him a vast network of supporters, instantly reachable through an unprecedented e-mail list of 13 million people. These supporters were not just left-wing activists but a broad coalition that included the young, African Americans, independents and even Republicans - and they were ready to be mobilized.

I worked as Obama's chief blogger during his presidential campaign, and my primary focus was telling the stories of these supporters, many of whom had never been engaged in politics or were reengaging after years of disillusionment. There was a common thread in my conversations with the hundreds of people who gave time, sweat and small donations - that amounted to $500 million - to Obama's campaign.

They were inspired by Obama's promise to upend Washington by governing from the bottom up. "The change we need doesn't come from Washington," Obama told them. "It comes to Washington."

Yet at seemingly every turn, Obama has chosen to play an inside game. Instead of actively engaging supporters in major legislative battles, Obama has told them to sit tight as he makes compromises behind closed doors.

During the battle over tax cuts, Obama's grass-roots network, Organizing for America, was silent. An OFA spokesman said that the network would engage supporters when the time is "ripe." But many people feel the time is ripe now - that tax cuts for millionaires in the midst of cuts in basic services and a spiraling deficit are unacceptable - and they don't understand why Obama won't let them fight.

During the health-care battle, rather than rallying the grass roots behind a public option - a provision Obama repeatedly supported and a clear majority of Americans backed - supporters were told to voice generalized support for "reform." In an e-mail from OFA, I was asked to call my senator, Chuck Schumer, a clear champion of the health-care plan that included a public option. Why not ask people to target centrist Democrats who were blocking reform, such as Max Baucus? It may have been counterproductive for me, a Brooklynite, to call a Montana senator's office, but at the very least I could have been asked to call OFA members in Montana and urge them to pressure Baucus.

Obama has made it clear that, for the most part, his administration isn't seriously interested in deploying this massive grass-roots list - which was once heralded as a force that could reshape politics as we know it - to fight for sweeping legislative change. It's a shame. In the few instances that the White House has meaningfully engaged the grass roots, OFA has shown that it has real clout. It's possible that the health-care bill, limited though it was, would not have passed were it not for decisive action from OFA in the final hours. When OFA members were finally asked to contact other Obama supporters in key legislative districts and after congressional offices were flooded with phone calls, letters and personal visits, several of the final holdouts in Congress were swayed to support the bill. Imagine if that aggressive, bottom-up approach had happened earlier in the process.

If the White House wants to keep its grass-roots supporters at bay during major legislative fights, that's its choice. But there's a larger problem looming.

Obama needs this list in 2012 - and he needs its members to dig much deeper than in the last election. The Citizens United ruling has allowed campaigns to become an unprecedented corporate cash free-for-all - and Obama will likely need to raise far more than $500 million from the grass roots to be competitive.

While Obama's political team intensely focuses on independents, the grass-roots list seems like an afterthought. Every time Obama chooses to compromise behind closed doors, and keeps OFA quiet, he might win over a few independents. But he's also conveying a message that the grass roots doesn't really matter, that the bottom-up ethos of his candidacy doesn't apply to his presidency.

On Thursday, Obama and White House staff met with a group of OFA volunteers who presented survey data and anecdotes on the state of the grass-roots base since the midterm elections. This is a positive sign, but the White House should move beyond gestures. Obama needs a senior adviser whose job is to be a liaison to the movement that elected him. This person needs to be in the room in senior-level strategy meetings, asking: How is this going to impact the list? What message will this send to the grass roots?

Obama needs twice as much grass-roots support in the next election - and he's not going to get it by sidelining his supporters. If he continues to play politics as usual, Obama risks alienating not just the left but anyone who believed in the promise of bringing change to Washington.

The writer is a new media consultant and freelance writer based in Brooklyn, N.Y.