One of the many ways that the election of Barack Obama as president has echoed that of John F. Kennedy is his use of a new medium that will forever change politics. For Mr. Kennedy, it was television. For Mr. Obama, it is the Internet.

“Were it not for the Internet, Barack Obama would not be president. Were it not for the Internet, Barack Obama would not have been the nominee,” said Arianna Huffington, editor in chief of The Huffington Post.

She spoke Friday about how politics and Web 2.0 intersect on a panel with Joe Trippi, a political consultant, and Gavin Newsom, the mayor of San Francisco, at the Web 2.0 Summit in San Francisco. (Karl Rove and Newt Gingrich had been invited to balance out the left-leaning panel, but declined, according to John Battelle, a chair of the conference.)

Howard Dean’s 2004 campaign -– which was run by Mr. Trippi –- was groundbreaking in its use of the Internet to raise small amounts of money from hundreds of thousands of people. But by using interactive Web 2.0 tools, Mr. Obama’s campaign changed the way politicians organize supporters, advertise to voters, defend against attacks and communicate with constituents.

Mr. Obama used the Internet to organize his supporters in a way that would have in the past required an army of volunteers and paid organizers on the ground, Mr. Trippi said.

“The tools changed between 2004 and 2008. Barack Obama won every single caucus state that matters, and he did it because of those tools, because he was able to move thousands of people to organize.”

Mr. Obama’s campaign took advantage of YouTube for free advertising. Mr. Trippi argued that those videos were more effective than television ads because viewers chose to watch them or received them from a friend instead of having their television shows interrupted.

“The campaign’s official stuff they created for YouTube was watched for 14.5 million hours,” Mr. Trippi said. “To buy 14.5 million hours on broadcast TV is $47 million.”

There has also been a sea change in fact-checking, with citizens using the Internet to find past speeches that prove a politician wrong and then using the Web to alert their fellow citizens.

The John McCain campaign, for example, originally said that Governor Sarah Palin opposed the so-called bridge to nowhere in Alaska, Ms. Huffington said. “Online there was an absolutely obsessive campaign to prove that wrong,” she said, and eventually the campaign stopped repeating it.

“In 2004, trust me, they would have gone on repeating it, because the echo chamber would not have been as facile,” Ms. Huffington said.

The Internet also let people repeatedly listen to the candidates’ own words in the face of attacks, Mr. Huffington said. As Reverend Jeremiah Wright’s incendiary words kept surfacing, people could re-watch Mr. Obama’s speech on race. To date, 6.7 million people have watched the 37-minute speech on YouTube.

The Internet also changes the way politicians govern. Mr. Newsom learned that last year when he ran for re-election. He showed up at a rally and didn’t see the usual crowd. His aides told him the audience was made up of his Facebook friends. “I said, ‘What’s Facebook?’” Mr. Newsom recalled.

These days, Mr. Newsom is “obsessed with Facebook.” It strengthens his connection with his constituents and their connection with the causes they care about, he said.

The constant exposure can, of course, turn against politicians.

Ms. Huffington’s “off the bus” team of 10,000 citizen journalists caught candidates saying things that embarrassed them later, like Mr. Obama’s “guns and religion” remark. Now, she said, “there is no off-the-record fund-raiser.”

Mr. Newsom says he is fearful of the constant need to watch his tongue. “I have to watch myself singing, ‘I left my heart in San Francisco’ on YouTube and it can’t go away. I am desperate to get it to go away,” he said dryly.

“There will be a lot of collateral damage coming to grips with the fact that we’re in a reality TV series, ‘Politics 24/7,’” Mr. Newsom said.

That’s a good thing, Mr. Trippi said. “This medium demands authenticity, and television for the most part demanded fake. Authenticity is something politicians haven’t been used to.”

He predicted that this real-time Internet contact with constituents will also change the way the president of the United States governs. He recently proposed that Mr. Obama start a Web site called MyWhiteHouse.gov to talk with citizens. (Mr. Obama just started a different site, Change.gov, on Thursday to keep in touch with people during the transition.)

“When Congress refuses to go with his agenda, it’s not going to be just the president” they oppose, Mr. Trippi said. It will be the president and his huge virtual network of citizens.

“Just like Kennedy brought in the television presidency, I think we’re about to see the first wired, connected, networked presidency,” Mr. Trippi said.