This theory is by no means foolproof. San Francisco Mayor Gavin Newsom, a Democrat, remains popular despite an affair with his campaign manager's wife. Former Sen. Bob Packwood (R-Ore.) was unseated in the mid-'90s amid groping allegations that would make Schwarzenegger blush. But it may well be that Republicans are better at using their opponents' sexual peccadilloes against them, summoning up the moral outrage among voters that can be deadly in a close race. It also doesn't help roving-eyed Democrats that women are a mainstay of the party, and women don't appreciate men who cheat. Villaraigosa, a Democrat who is...