July 13 (Bloomberg) -- San Francisco Mayor Gavin Newsom is running for re-election virtually unopposed, more popular than ever, after admitting to having an affair with a top aide's wife and entering an alcohol-treatment program.

Newsom, whose approval ratings are running close to 80 percent, said he expects a credible candidate to emerge eventually. So far, challengers include a street-performing clown, a homeless man, an advocate for nudism, and a candidate who pledges to wear a camera so voters can monitor his performance in office.

``We haven't seen anything like this in a very long time,'' said David Binder, a pollster who has tracked San Francisco politics since the early 1980s. It's becoming one of the oddest elections in 25 years in a city known for making incumbent mayors endure bruising campaigns, he said.

In 1983, Dianne Feinstein, now a U.S. senator, fought off a recall campaign as mayor. Her successors, Frank Jordan and Art Agnos, were defeated after just one term. In 1999, Democrat Willie Brown used a rare endorsement from Republicans to win a second term.

Newsom, a 39-year-old Democrat, squeaked by in the 2003 election. Backed by Feinstein and House Speaker Nancy Pelosi, he trailed a Green Party opponent Election Day and was declared the winner after absentee ballots were counted.

Newsom bolstered his image in the city 3 1/2 years ago by issuing marriage licenses to same-sex couples. He's a restaurant owner who calls himself a pro-business Democrat who's ``extraordinarily progressive on social issues.''

Admitting an Affair

Newsom needed the popularity to weather his scandals. On Feb. 1, he held a news conference to admit having an affair with his secretary, who's the wife of his campaign manager and then- chief of staff.

Hours after the San Francisco Chronicle reported the affair, Newsom made a public apology that was nationally televised. He told viewers: ``Everything you've heard is true.''

A few days later, he entered an alcohol-treatment program and survived a call for his resignation. Newsom said the affair was the climax of a ``brutal'' period that included losing a bid for the 2016 Summer Olympics and the San Francisco 49ers football team saying it might move to Silicon Valley.

``I dealt with it, at least to the extent that I could, in a very forthright and honest way and didn't try to excuse it, and didn't try to nuance it,'' he said in an interview last week. ``That allowed us to move on after some very difficult weeks.''

No Advantage

The scandal hasn't offered a leg up to his enemies. Even after city progressives held a convention to pick a liberal challenger to run in the Nov. 6 election, no candidate emerged. The city doesn't hold a mayoral primary.

Newsom is frequently mentioned, along with Los Angeles Mayor Antonio Villaraigosa, as a potential successor to Governor Arnold Schwarzenegger in 2010 or as a U.S. senator. Villaraigosa, too, faces a sex scandal after admitting an affair with a television reporter.

Binder said Newsom's decision to allow weddings for gay couples was unprecedented, setting up his image as the ``people's mayor.'' It was a contrast to his initial portrayal by critics as a ``rich kid who had everything handed to him and didn't understand the struggles of the city,'' Binder said.

Gay marriage ``brought into his camp a lot of gays and lesbians and progressives who hadn't been supportive of him,'' Binder said.

The gay community has a high voter turnout rate and gives Newsom a fund-raising and volunteer base, said Scott Wiener, chairman of the San Francisco Democratic Party and former chairman of the Alice B. Toklas LGBT Democratic Club, one of the oldest U.S. voter organizations representing lesbians, gays, bisexuals and transgenders.

``Gay marriage showed that he was willing to take leadership on issues that were very controversial,'' Wiener said.

Unique Standards

Brown, the former mayor and Assembly speaker, said gay marriage and a proposal to provide health care for the uninsured created for Newsom an image that's ``totally acceptable'' in San Francisco ``no matter what the rest of his politics may be.'' His public relations savvy has been superior to his predecessors', Brown said.

Sex scandals at City Hall are nothing new. In 2001, Brown had an out-of-wedlock child with his top fund-raiser.

``San Francisco is a city-state unto itself,'' said Rich DeLeon, professor emeritus at San Francisco State University and author of ``Left Coast City,'' a 1992 book about the city's politics.

``The same things that get people upset around the country about personal morality -- sexual issues -- are not a big issue here,'' DeLeon said. ``It would sound strange to get morally righteous here.''

Board Clashes

Newsom has frequently clashed with the city's 11-member Board of Supervisors. Local and national news outlets carried accounts when Supervisor Chris Daly referred at a meeting last month to ``cocaine use'' by the mayor. Newsom, in the interview, said the charge is ``gratuitous.''

Board President Aaron Peskin said Newsom's popularity is ``an inch deep and a mile wide.'' The mayor's biggest moves either were symbolic, such as marching with locked-out hotel workers, or co-opted ideas backed by the board, such as health care for 82,000 uncovered residents, he said.

``People like him,'' Peskin said. ``But when you ask them what he's done, all they would probably say is gay marriage.''

To contact the reporter on this story: Adam Satariano in San Francisco at Asatariano1@bloomberg.net

Last Updated: July 13, 2007 02:58 EDT