SAN JOSE, Calif. – A rogue’s gallery of philandering politicians in recent years has illuminated an essential political truth: Not all sex scandals are created equal.

From President Bill Clinton to Bay Area mayors Gavin Newsom and Ron Gonzales, from U.S. Sens. John Edwards and Larry Craig to New York Gov. Eliot Spitzer – and now South Carolina Gov. Mark Sanford – the effects of sexual wrongdoing are highly unpredictable.

Some political careers are destroyed. Some are rocked but recover. Others seem to bob and weave but go on essentially unscathed. The harshest outcomes seem reserved for behavior “a la Sanford” – deemed both weird and hypocritical.

“It’s all about expectations,” said Gregory Rodriguez, senior fellow at the New America Foundation, a nonpartisan think tank. “The fortunes of any given candidate really depend on our expectations of that person at any given moment and on the candidate’s own rhetoric and sense of righteousness.”

Willie Brown, the former San Francisco mayor and California Assembly speaker, for example, “would sort of wink at the public and we sort of loved it” because Brown, famously a social butterfly, “could get away with a lot of things because he didn’t come off as self-righteous,” Rodriguez said.

But when politicians say one thing and do another, the “hypocrite” tag can be a killing blow to a career.

Spitzer, a Democrat who played the public role of righteous law man, broke the law by spending tens of thousands of dollars on call girls. Republicans Sanford and Nevada Sen. John Ensign, who earlier this month disclosed an affair with a campaign aide, also face a harsher judgment because both politicians had severely criticized Clinton for his infidelities. A charge of hypocrisy was also tossed at former Sen. Craig, a conservative Republican from Idaho who voted against gay-rights legislation but got caught trolling a men’s room for sex. His political career went down the toilet.

Sometimes the particulars surrounding an affair are just too much, even for an ever more cynical public.

Edwards, a former North Carolina senator who sought the Democratic nomination for president, sold the whole “perfect family” story line. Then it turned out he had cheated on his courageous wife after she was diagnosed with breast cancer.

Los Angeles Mayor Antonio Villaraigosa probably pre-paid a steep political price by announcing he would not run in the Democratic gubernatorial primary. He has been forced to confess that he was dating a TV reporter before his marriage broke up. On the other hand, San Francisco Mayor Newsom’s confessed affair with the wife of one of his best friends didn’t stop him from jumping into the race.

At one time, some political analysts had said that former San Jose Mayor Gonzales had a good chance of becoming California’s first modern-day Latino governor. Then he had an affair, publicly lied about it and disgraced his sunny and popular wife by running off with the younger woman. Further damaged by a garbage contract scandal, Gonzales is now a forgotten blot with absolutely no future in politics.

But if a politician is simply caught with his pants down – and there are no other sleazy or bizarre allegations – do most Americans care?

Not really, says Brown. “I think the public still measures politicians and elected types as to how they perform their core responsibilities,” he said.

It’s only natural, Brown said, that conservative Republicans such as Sanford will be held to a higher standard because they are “plagued with a constituency that demands alleged purity.”

Often the relevance of an exposed affair depends on a voter’s religious values.”I’m an Irish Catholic who grew up in Jesuit land, so the importance of fidelity is part of who I am,” said Barbara O’Connor, director of the Institute for the Study of Politics and Media at Cal State-Sacramento.

Hit with sex scandal after sex scandal, the public often asks: Just what were these guys (and they are almost always guys) thinking?

Pundits say it isn’t much of a mystery.

Surrounded by sycophants and security bubbles, “these guys really become convinced that the laws of ordinary mortals do not apply to them,” said Sherry Bebitch Jeffe, a veteran political analyst at the University of Southern California who has labeled the phenomenon “PPS” – professional politician syndrome.

Sanford’s image was severely tarnished by a week of weirdness: He abandoned his wife and four sons around Father’s Day, giving rise to a fairy tale about him “hiking the Appalachian Trail” to get some time alone. Not only was he 5,000 miles away with another woman, but also their intimate e-mails are now on international public display.

Whether or not philandering politicians survive politically, sex scandals almost always leave deep scars.

“One might say that President Clinton was able to rehabilitate his career, but it was a rehabilitation that occurred largely after his presidency, by the impressive charitable work he has done around the world,” said Doug Kmiec, former counsel for Presidents Ronald Reagan and George H.W. Bush.

“It was more this than it was people forgetting what he did,” said Kmiec, now a professor of constitutional law at Pepperdine University.

But what about Newsom? He seems to have weathered his own squall of bad press after he publicly confessed his affair in 2007. And Brown doesn’t think the scandal will affect Newsom’s ambitions to become the next governor. “Who’s going to bring it up?” Brown asked.

Kmiec, however, believes the Newsom scandal may have a longer shelf life: “I also suspect his opponents will be taking full advantage of that infidelity as part of their campaigns.”

Still, it may be the more self-righteous – and predominantly Republican – bad boys who should most fear the public’s wrath. Candidates who wrap themselves in sanctimony – and end up doing dastardly deeds – usually fall the hardest.

“It’s this inherent contradiction that we require our politicians to act holier than thou,” said Rodriguez of the New America Foundation. “But at the same time we expect them to screw up. It’s a weird drama of our own making.”