Updated | 4:20 p.m. The Obama campaign’s willingness to have supporters communicate and strategize with each other online, rather than wait for commands from on high, has been credited with giving him a crucial advantage over opponents who favor more traditional political tools. Nothing better typifies this strategy of letting the grass-roots grow on the campaign headquarters’ front lawn than its popular Web portal, my.barackobama.com, where supporters can form groups and create blogs.

But in the last week, my.barackobama.com has also become an excellent place for supporters to gather and discuss their disappointment with their candidate, surely a new development for a campaign fueled by popular enthusiasm, particularly online.

The rallying cry has been Mr. Obama’s support for a revised version of the Foreign Intelligence Surveillance Act that includes immunity to lawsuits for phone companies over their role in assisting in the Bush administration’s warrantless wiretapping program.

A group on my.barackobama.com with the polite name “Senator Obama­ Please Vote NO on Telecom Immunity –­ Get FISA Right” is now the fourth-largest public group at the portal, and it is growing fast. The mission statement on my.barackobama.com is, as follows: “We are a proud group of your supporters who believe in your call for hope and a new kind of politics. Please reject the politics of fear on national security, vote against this bill and lead other Democrats to do the same!”

The vote on FISA in the Senate has been delayed until after the July Fourth holiday.

The group, created on Wednesday, has more than 8,000 members, and recently passed the group “Women for Obama.” (On Monday morning, there were barely 4,000 members of the anti-FISA group.)

It is worth noting, however, that much of the networking among Mr. Obama’s supporters lives outside of the campaign’s walls. The largest group on my.barackobama.com, Action Wire, has about 13,400 members, while Mr. Obama’s Facebook page has more than 1 million supporters.

The entire episode shows the potential complications of an open site becoming an enabler of criticism from ardent supporters, let alone from opponents in disguise, so-called “concern trolls.” ­ But the campaign said it wouldn’t have it any other way.

In an e-mail message, Tommy Vietor, an Obama campaign spokesperson, wrote: “This campaign has an extraordinary group of committed supporters, and we greatly appreciate their willingness to share their time and ideas with us. We believe that an open dialogue is an important part of any campaign, and are happy that my.barackobama.com has become a vehicle for that conversation.”

The group was conceived on a listserv for progressive, politically active people, said Mike Stark, an activist who is a law student at the University of Virginia. He wrote an initial e-mail to the group arguing: “Obama is getting mad props for social networking, why don’t we use social networking to let him know that he can’t keep elbowing his progressive base — the people who got him the nomination — away from the policy table?”

One of the recipients, who was already a member of my.barackobama.com, created the group. There were bumps in membership when various blogs wrote sympathetically, Mr. Stark said, but, “the biggest bump was from the members themselves.” He called it “the networking effect.”

The idea that the site would reject the sub-group never occurred to him, he said, because of Mr. Obama’s commitment to using the Internet to bring more transparency to government. “One of his key things is a five-day comment period before he signs noncritical legislation, and not all of that comment will be favorable,” he said. “It’s a test run to see what his presidency might look like.”

Mr. Stark said he was thinking beyond the FISA vote, which he concedes is all but lost. He said he planned to change the group’s name to Barack’s Better Angels, and linger at the site until the election as a meeting place for “progressives who won’t accept being pushed away from the table.”