In a VIP room, Mr. Paxton was relating a story to Mr. Obama’s California campaign manager, Mitchell Schwartz, about an awkward encounter he had with real-life Mormon Mitt Romney.

“He gave me what I call the heave-ho handshake,” said Mr. Paxton, taking Mr. Schwartz’ hand and slinging himself forward to show the way Mr. Romney had rudely dispatched him. Mr. Schwartz, wearing a security-clearance pin on his lapel, laughed and matched Mr. Paxton’s handshake impression with one of his own, making fun of Bill Clinton’s roving eye.

Mr. Paxton offered his services to the campaign, saying he would appear on television, hit the streets or do whatever else needed doing. Mr. Schwartz added him to the list.

In California, celebrity is the companion piece of presidential politics, with the Democratic candidates themselves advertised and evaluated like box office rivals.

This week, as the California primary emerged as the hyper-competitive lodestar of the Super Tuesday states, picking a Democratic nominee became the only project with any buzz.

The Democratic debate last week at the Kodak Theater had all the trappings of an awards show. As Mr. Obama and Mrs. Clinton performed onstage, the cameras cut to Lou Gossett Jr. and Steven Spielberg and Jason Alexander nodding meaningfully at their words. Fran Drescher, at one point, gave a thumbs-up when Mr. Obama and Mrs. Clinton pretended to like one another.

When the debate ended, the celebrities spilled into the red-carpeted lobbies while above them, on the third floor, reporters heard from campaign advisers and surrogates in a makeshift spin room. Jonathan Pontell, a professional public speaker with Kato Kalin-like orange hair, instructed a woman in a short red dress (“My name is Citizen Kate, I have my own Web log!” she said) on how to sneak down to the lower level to, as he put it, “schmooze the Hollywood socialites and stars and directors.”

Gavin Newsom, the mayor of San Francisco and a Clinton supporter with a Hollywood jaw line and slicked hair, talked about the “buzz, energy, youth, vibrancy” that celebrities lent candidates in Los Angeles. “There is an edginess. All those things. The creative index of life. There is a vibe that’s created, whether you like it or not, when Barack is there with an Oprah Winfrey. There is a vibe that’s created when there is a Leo.”

“We want to see celebrities,” explained Los Angeles Mayor Antonio Villaraigosa, as he slipped out the back door.

On the lower levels, the celebrities critiqued the evening’s performances.

“Especially as an actor, you read a lot into people’s behavior and how they deal with uncomfortable moments,” said Richard Schiff, a member of the president’s cabinet on The West Wing. He added, “It is better than any reality television out here.”

“What do you think?” he said to his friend Steven Weber, who played one of the brothers on the 1990’s sitcom Wings, and who had stepped into an elevator with him.

“Politicians are performers, they have to act their messages,” said Mr. Weber. “They have to embrace a text.”

Inside the club for the post-debate Obama fund-raiser, Mr. Obama first shook hands with supporters in a special reception room, where Kareem Abdul-Jabbar pushed aside shorter supporters to get some face time with the candidate. Mr. Obama then addressed a larger crowd from a stage in front of a giant banner that said “Change.”

“And by the way, when I made that proposal, I didn’t do it in front of the Sierra Club, I didn’t do it in front of this crowd in Hollywood,” he said. “I did it in Detroit in front of the automakers.”

He was, unsurprisingly, a hit. Quentin Tarantino, who wore a snakeskin suit and long pointy shoes, clapped and hooted exuberantly. Greg Germann, who acted on the show Ally McBeal, said Mr. Obama “digs deep.” Joe Mantegna, who described himself as undecided, said the whole town had been energized by the Democratic race.

“I’m old enough to have been around for Kennedy and the whole thing and this reminds me of that,” he said of Mr. Obama. “It’s kind of like Camelot.”

There was a lot of that.

Mr. Paxton, who had arrived late, made his way into a private room decorated with Spanish tiles and wound up talking to an audience of entertainment lawyers, lighting designers, bloggers and publicists about a project he was working on for HBO, about John F. Kennedy’s last days.

As he made comparisons to the charisma of Mr. Obama and Kennedy, R. J. Cutler, who produced The War Room, a documentary about Bill Clinton’s successful 1992 campaign, nodded in agreement.

Mr. Cutler, referring to the effectiveness of this year’s Clinton war room against Mr. Obama, said, “I think they can stop him, but imagine if they didn’t stop him—imagine what world that would be like.”

Later, Mr. Paxton led a group of Obama supporters out of the club down the block to Katsuya, a new Philippe Starck-designed Japanese restaurant. Along the way, he described why he had committed to Mr. Obama, who he heard speak for the first time at a fund-raiser about three weeks earlier.

“I turned off to politicians and the whole scene for so long, and then this guy comes along,” he said, as he walked over a star on the Hollywood Walk of Fame dedicated to Red Buttons. He said he was depressed by the cynicism his children expressed about the office of the president. “That’s horrible,” he said. “Idealism is the bastion of youth.”

“But this guy, he feels presidential,” he said.

A few paparazzi stationed outside the restaurant snapped his picture.

“I can see him in the world theater. I can see him with world dignitaries,” he continued. “Again, I don’t need to do this stuff. I got a nice career. I don’t need to lay it on the line for anybody. I just find that I want to get behind this guy, I really do.”

“Can we get in here?” he said, walking up to the hostess of the restaurant, which seemed booked solid. “Thanks.”

A little while later, a Japanese woman sat Mr. Paxton’s party in a small, private room partitioned from the rest of the eatery by a white curtain. They ate salmon with caviar, beef and foie gras, onion-encased halibut and a variety of sushi.

“All of us are sitting around the table tonight for one reason,” said Mr. Paxton to his fellow Obama supporters. “And that’s pretty cool.”

Late in the night, as Mr. Paxton drove through Silver Lake and Echo Park and detoured to a small hill with a view of downtown Los Angeles, he pointed out buildings in front of which Buster Keaton performed his pratfalls, and streets where Chinatown was filmed, and where the “best tacos in North America” are served, and where you would not want your car to break down. Throughout the tour, he kept coming back to his admiration for Mr. Obama, repeating, “Idealism is the ba
stion of youth.”

ON THE MORNING of Feb. 1, Hillary Clinton began campaigning with an entourage of supportive California elected officials, eliciting roars of approval in sprawling gyms and convention centers in Los Angeles, San Diego and San Jose from the largest and loudest and youngest crowds she has drawn this entire campaign season. At her last stop of the day, in San Francisco, Mrs. Clinton deployed her own celebrity endorsements.

An effusive, now-white-haired Ted Danson introduced her on the stage of the ornate Orpheum Theatre as a “sympathetic, warm, wise, beautiful woman.” His wife, the actress Mary Steenburgen, wore a black dress and shimmering black boots up to her knees and testified that Mrs. Clinton’s “belly laugh is more raucous and dirty than mine, which is saying something.”

When the surrogates stepped off the stage, Mrs. Clinton stood alone and delivered a detail-packed policy speech.

For her last event in California, the following morning, in a gym at the State University of California in East Los Angeles, the Clinton show started with live music performed by the Mariachi Divas (organizers asked them to leave before Mrs. Clinton actually spoke) and celebrity warm-up acts.

Sally Field, dressed in a beige jacket and glasses, pronounced herself blown away. “I have been overwhelmed by how precise and specific her answers are,” she said.

Bradley Whitford, another West Wing actor, said, “I’m supporting Hillary because she has a dirty uniform.” Magic Johnson declared that with Mrs. Clinton as president, “all the world will be happy because all the world will know that America is open for business.”

“We have an amazing constellation of California stars right here,” Mrs. Clinton declared.

After the event, J. T Mollner, a 29-year-old director and Clinton supporter wearing a wool cap and striped sweater, said, “Celebrities give candidates a hip factor. Unfortunately, that is necessary to win.”

After Mrs. Clinton left California, her campaign notified reporters that her biggest celebrity supporter, Bill Clinton, would return before Tuesday’s voting.

AT BARS AND house parties throughout Los Angeles, the beer-fueled conversation focused as much on the tightening California race between Mrs. Clinton and Mr. Obama as on new “projects” or meetings taken. Even paparazzi magnets like Lindsay Lohan, who ate a bowl of soup at Toast on Third Street Saturday afternoon, were for the most part left alone. (“I’m not sure yet,” she said when asked—annoyingly, by this reporter—who she planned to support.)

At a party of independent filmmakers on the night of Feb. 2, one woman said she was sick of everyone talking about Mr. Obama. Another woman who managed writers marveled at Mrs. Clinton’s endurance, but wasn’t sure she wanted to see her in the White House again. A former assistant to Oprah Winfrey stressed how enthusiastic her old boss was for Mr. Obama’s candidacy.

On the morning of Feb. 3, a Sunday, the full power of Ms. Winfrey’s celebrity revealed itself inside the Pauley Pavilion at UCLA, where she was set to make an appearance with Michelle Obama and Caroline Kennedy. As thousands of women filed in—the actor Michael York lazily held an Obama sign in the bleachers—a Jumbotron above the stage showed a music video featuring Scarlett Johansson, Common, will.i.am and Fresh Prince actress Tatyana Ali singing along to Mr. Obama’s “Yes We Can” speech.

When Ms. Winfrey appeared, dressed in a white shirt and black jacket and pants, the thousands of self-proclaimed “Obama mamas” broke out into pandemonium.

“We are free from the constrictions of gender and race and we can vote as we believe,” she said, adding, “I’m just following my own truth. And that truth has led me to Barack Obama.”

The audience, to judge by its raucous reaction, was impressed.

“She’s an important person and has quite a following,” said Chris Oshima, a judicial assistant from Los Angeles who was in the crowd. “She’s the embodiment of following your own dreams and your own thoughts.”

A few minutes later Ms. Obama came out and spoke, and then, in a surprise, so did Maria Shriver.

But first, Ms. Obama had another tinsel-wrapped present to give.

“Let’s give it up,” she said, “for Mr. Stevie Wonder!”