NEW YORK - Five days after Sen. John McCain named Alaska Gov. Sarah Palin as his running mate, Quinn Latimer and co-worker Lyra Kilston sent an e-mail to 40 female friends and invited them to outline the reasons they were upset with his choice. It elicited such a huge response -- from friends of friends and utter strangers -- that they created a blog called Women Against Sarah Palin. In less than a month, it has become one of the largest hubs of online opposition to Palin, receiving more than 160,000 e-mails.

MoveOn members "tell us where to go. They lead us," says Eli Pariser, the group's executive director. (By Helayne Seidman For The Washington Post) "I am a fiscally conservative, socially liberal Republican," writes a 65-year-old from Flagstaff, Ariz. "I am aghast at the choice the Republican ticket has made."

"As a registered Independent, I'd been holding out in deciding which way to go on this election. However, once I saw Sarah Palin being interviewed . . . it was a much easier decision," writes a 52-year-old from Los Angeles.

Along the way, Latimer got an e-mail from Eli Pariser, head of the liberal group MoveOn.org. Pariser knows about e-mail campaigns; he built MoveOn around them. And Latimer has been a member of the organization since 2000. When Pariser found out that Latimer and Kilston also live in Brooklyn, he asked them to brunch at Flatbush Farm, a local hot spot. Over eggs, oatmeal and coffee, he offered technical support from MoveOn. At one point, he even suggested that the women take time off from their jobs and work full time on the blog until Nov. 4. MoveOn, Pariser told the women, could raise the funds to pay them.

"I got to admit I was shocked by that," says Latimer, 30, an art editor.

Adds Kilston, 31, also an art editor: "We just kind of stumbled into this whole blogging thing."

The women decided to keep their jobs while maintaining the site. But now, with help from MoveOn, they'll use the e-mail list of everyone who has sent a note to the blog to send information about voter registration, phone call drives and house parties. And, to match their online activism, Latimer and Kilston plan to knock on doors for Sen. Barack Obama in Pennsylvania.

MoveOn, the enfant terrible of online politicking, is growing up, turning 10 years old last month. And it has become far more than a purveyor of vituperative e-mail blasts. During the 2006 midterm elections, for instance, the online organization -- with a full-time staff of 23, most of whom work from home -- spent $28 million advocating for Democratic candidates through its political action committee, according to the nonpartisan Center for Responsive Politics. In contrast, the National Rifle Association, with a staff of about 500 housed in its expansive headquarters in Fairfax, spent $11 million through its PAC.

As the battle between Obama and McCain heated up this summer, MoveOn witnessed its largest increase in membership -- adding a million new members in three months, bringing its total to 4.2 million.

Not bad for a group that started off as an online petition to stop the impeachment of President Bill Clinton. Created in September 1998 by Silicon Valley entrepreneurs Wes Boyd and Joan Blades, the petition asked Congress to censure Clinton and "move on" to other domestic issues.

"At first, we weren't sure what to make of MoveOn," says Paul Begala, then a senior aide in the Clinton White House. "But it became clear that the grass-roots power that MoveOn represents is what helped save us." In the years since -- through the group's virulent opposition to President Bush and the Iraq war -- Begala has regarded MoveOn as a "spinal transplant" that has reinvigorated the Democratic Party.

Perhaps that's an exaggeration. Democrats, after all, lost the White House in 2000 and 2004. It wasn't until the 2006 midterms that they controlled Congress. Still, political operatives in both parties agree that MoveOn is a singular force in Washington, unmatched in its reach and resources. For years, some Republicans have tried to create their own version of it, with little success. At the Republican National Convention in St. Paul, Minn., last month, Tom DeLay, the former House majority leader, bemoaned that the right has "nothing that looks like MoveOn.org," adding that the GOP is "still in denial about what the left has been able to do."

But what exactly is MoveOn?

Although it's not a formal arm of the Democratic Party -- and the group doesn't rule out endorsing and financing third-party candidates -- MoveOn has become synonymous with the party's left wing. It's not technically a lobbying group: MoveOn doesn't employ lobbyists who've mastered the ins and outs of Capitol Hill. It's more akin to an interest group, a la Emily's List, the pro-choice organization that supports like-minded female politicians, although Pariser says somewhat grandiosely, "We are not about serving our members' individual interests -- we are primarily serving a national interest." And though officials like to say that MoveOn's membership is as sizable as the NRA's, signing up to receive the group's e-mails is not the same level of commitment as paying dues to the gun rights organization.

But in an online networking era in which pols promote their e-mail lists as a symbol of their grass-roots strength, MoveOn's list is unlike any other.

The group is led by Pariser, a tall, lanky self-described computer geek, who grew up in Lincolnville, Maine, and graduated at 19 from Simon's Rock, a small liberal arts college in western Massachusetts. "Led" is a verb that Pariser would take exception to. The way he sees it, MoveOn members are in charge. "They tell us where to go. They lead us," the 27-year-old says of his organization. "It's not about having anointed leaders. It's about leveraging technology so people can help lead themselves."

He points to regular surveys that MoveOn conducts to take the pulse of its membership. One week, members deem getting a 60-seat, filibuster-proof Democratic Senate majority as a top priority. The next, eyes turn to the financial bailout plan. When MoveOn members voted to endorse Obama over Sen. Hillary Clinton days before Super Tuesday on Feb. 5, it was up to Pariser to call and tell Patti Solis Doyle, who was then Clinton's campaign manager.

At the Democratic National Convention in Denver, where MoveOn hosted a packed soiree attended by the likes of San Francisco Mayor Gavin Newsom and comedian Sarah Silverman, the group seemed part of the very establishment that it criticizes -- a charge that Pariser rejects. To the McCain campaign, Obama and MoveOn are inseparable. "It's hard for Obama to claim any pretenses of bipartisan outreach when he gladly accepts the help of partisan special-interest groups like MoveOn.org," says McCain spokesman Alex Conant.

Pariser's political activism also began with an e-mail. After the Sept. 11 attacks, he sent a note to a group of friends, urging them to contact their elected officials and ask for a restrained response to the tragedy. The e-mail turned into a petition, eventually signed by more than half a million people online. Two months later, MoveOn called with a job offer.

Guided by Pariser, MoveOn began to make its mark by raising money online -- lots of it.

"When we started MoveOn, there was this standard model of how candidates are elected. Say I'm a candidate and you're a political consultant. You put me in a room, you give me a list of rich donors to call, I make calls and raise, what, $2,000 checks. Then I hand the $2,000 checks to you. You make ads with it. You take a healthy cut. You put those ads in the air -- that's how elections are won. At no point during that process does it matter to anyone other than the rich donors what you actually stand for," Pariser says.

"There's a different model now. It was the [Howard] Dean model. It's now the Obama model. You can say things that inspire people and get lots of people to contribute just a little bit. Twenty. Fifty. Maybe, who knows, even a hundred. Then instead of being accountable to a small set of rich donors, you're accountable to a large set of everyday donors."

The money has afforded MoveOn so much pull that it's hard to find a prominent Democrat who will openly criticize the group's tactics and positions. "Elected officials don't want to offend them and lose their money, right?" says a party strategist who refused to be identified. MoveOn, he adds, "is like a big-party donor, so they get treated that way. . . . A lot of people in the party who used to have more power don't like that they are losing juice to the likes of MoveOn, but they also realize they can't have the power they have without them."

Throughout this campaign cycle, MoveOn has raised nearly $33 million and expects to hit $38 million before Election Day -- money spent buying ads for and against candidates and funding get-out-the-vote efforts. All that money has led to more influence. And to more criticism when the group stumbles.

For instance, MoveOn was repudiated by Republicans and Democrats alike in September 2007 when the group ran an anti-war print ad in the New York Times that questioned the integrity of Gen. David Petraeus, the commander in Iraq. "General Petraeus or General Betray Us?" read the ad. Republicans introduced resolutions condemning the ad that easily passed in both the House and Senate.

Pariser defended it at the time. But now, more than a year later, he says he "would have worded the ad differently."

"MoveOn is still evolving, still maturing, still learning what its boundaries are," says Tad Devine, a longtime Democratic consultant. "But make no mistake about it: This election might be decided by a few votes in a few states. . . . Having those hundreds of thousands of people communicating with each other through e-mails, energizing the base, can make the difference."

On Aug. 29, just hours after the Alaska governor became the first Republican woman on a national ticket, MoveOn sent an e-mail to its members titled "Who is Sarah Palin?"

"Yesterday was John McCain's 72nd birthday. If elected, he'd be the oldest president ever inaugurated," read the e-mail. "And after months of slamming Barack Obama for 'inexperience,' here's who John McCain has chosen to be one heartbeat away from the presidency."

That became one of the most forwarded e-mails in MoveOn's history, Pariser says. (The group can count how many people click on the link in the e-mail.)

Two weeks later, on Sept. 10, MoveOn sent another e-mail, this one titled "Disgusting."

"John McCain and Sarah Palin are repeatedly deceiving, manipulating, and flat-out lying. And polls are showing that some of those lies are convincing voters," the e-mail began. "Palin says she opposed the 'Bridge to Nowhere' -- when in fact she fully supported it. McCain says Obama wants sex-ed for kindergartners -- when he voted for a bill to protect them from sexual predators."

That e-mail raised $1.2 million within 24 hours, Pariser says, the most a MoveOn e-mail has raised in a single day.

"In a way, Palin's selection was yet another wake-up call, another reminder of just how high the stakes are," says Pariser. "A lot of people have said that she's energized the evangelical base. Well, she's energized the liberal base, too. Our energy level went way, way up."

The challenge for a maturing organization is to move beyond forwarding e-mails and facilitating online donations. Can MoveOn persuade independents and Republicans to cross party lines? Is it increasing voter turnout in swing states? How can it avoid being reduced to parody? A recent headline in the Onion, for instance, read "Obama Deletes Another Unread MoveOn.org E-Mail."

Those are the questions in the minds of critics such as Clay Shirky, author of "Here Comes Everybody: The Power of Organizing Without Organizations." Sending an e-mail to your congressional representative is so easy that it has "become effectively meaningless," writes Shirky.

Shortly after the book came out, Pariser asked Shirky to lunch. On the day of the meeting, Shirky Twittered: "I'm going to lunch with MoveOn. If I don't Tweet again in two hours, they had me killed."

"Eli sees MoveOn as a community-organizing platform that happens to run e-mail campaigns," says Shirky, recalling the conversation. "I'm inclined to think of them as a message and fundraising organization that does some community organizing. They do some, but they can do so much more."

In the past five years, Pariser has beefed up the group's offline strategy. In addition to airing pro-Obama TV ads, the group will spend about $5 million in field efforts this cycle.

MoveOn collaborates with political scientists at Yale who are studying the impact of its canvassing and get-out-the-vote efforts in 2004 and 2006. In 2004, about 70,000 members went door to door in 12 states trying to increase voter turnout. This year, Pariser estimates that about 200,000 will have gotten involved by Election Day in more than a dozen states.

MoveOn is also holding hundreds of "Call for Change" house parties, at which members call voters in swing states. On a recent Sunday night, MoveOn members made half a million phone calls in two hours. They urged supporters to volunteer for the Obama campaign -- and, in classic MoveOn style, posted photos on Flickr of themselves talking on their phones.

"I give it a 55-45, with Obama winning," Pariser says from behind his standing desk in his home office. Thomas Jefferson and Donald Rumseld, he notes, had standing desks. "I somehow picked up that trivia."

He got up at 6:20 a.m. on this late September day, went to back-to-back meetings in the afternoon ("with other online advocacy groups," he says, repeatedly declining to elaborate), then hurried home, which is a cramped two-bedroom apartment in Brooklyn where he sometimes has to jiggle the toilet handle to make sure the water stops running. He lives with his wife, Lindsay, a human resources manager for a construction firm. They married in June.

"When I told people that MoveOn turned 10 today, many said, 'What? Ten years ? It feels like it was yesterday,' " says Pariser.

"But to me, it feels like it's been decades since 2001 when I first started getting involved. That was such a different world. In 2001, online organizing wasn't really on anyone's radar. There was no YouTube. No Facebook. No group of liberal bloggers, no Net roots. And Bush? Bush was absolutely ascendant. . . . The Democrats were in absolute disarray."

"Don't get me wrong -- a lot can change between now and November 4th. Obama can lose," Pariser says. "But here's the thing: Independent of the Obama campaign, in our own lives, through our own networks, we're doing everything we can to win this election. Back in 2001, people felt alone, like there was nothing you could do to get involved. Not anymore. People are finding each other. People are communicating. People are pumped up.

"What happens in our in-boxes doesn't just stay there."