He left his career in... San Francisco

Here's a mistake Gavin Newsom, the Mayor of San Francisco, won't be making again in a hurry: sleeping with the wife of his campaign manager.

Mr Newsom, a charismatic politician often mentioned as a future candidate for much higher office, has admitted having an affair with Ruby Rippey-Tourk. Not only is Ms Rippey-Tourk married to Alex Tourk, one of the Mayor's best friends who was managing his re-election campaign, at the time of the affair, she was also his appointments secretary - so he committed one of the cardinal sins of public life by having sex with an employee.

This being San Francisco, the scandal has provided amusement more than moral outrage - although Mr Tourk, for one, is no longer on speaking terms with the Mayor and has resigned from his job.

Most seriously, it has raised questions about Mr NewsomÕs political future, not least because he has an unfortunate habit of letting his love life dominate the front pages of the city newspapers. Ever since Mr Newsom split up with his glamorous wife, a Fox News host called Kimberly Guilfoyle, he has been seen consorting with a 19-year-old model - who may or may not have been drinking under age while out in public with him - and with a Hollywood actress, Sofia Milos, who invited him to a Scientologist dinner party in Los Angeles.

The brief affair with Ms Rippey-Tourk appears to have taken place just as he was going throught the throes of his divorce.

None of this is likely to dent his chances of re-election this year - a healthy majority of San Franciscans think he has done a good job. But Mr Newsom is providing ever more fodder to heartland conservatives and talk-radio hosts who like to denounce "San Francisco values" that, they say, are wrecking the nationÕs moral fibre. Even some of Mr NewsomÕs fellow Democrats are furious with him for sanctioning gay marriage for a few brief months in 2004 - arguing that he triggered a national backlash against his party that allowed President Bush to win a second term in the White House.

One of those Democrats, top consultant Jack Davis, said last week: "Gavin should resign and seek psychiatric help." Not that Mr Davis is a paragon of virtue: a decade ago, he invited every luminary in town to a notorious 50th birthday party at which two strippers urinated on each other and performed unspeakable sexual acts with a Jack Daniels whiskey bottle.