So Barney Frank's career survived his romp with a male prostitute, while John Edwards' fling with a campaign aide made him politically radioactive. Sex without marriage is OK. Sex in violation of marriage is not.

Why not? Because adultery, unlike a frisky bachelor lifestyle, connotes a reckless dishonesty at odds with our basic notions of integrity. Because it shows a lack of respect for the most important commitment that most of us will ever make. Because it indicates that the adulterer will always place his selfish desires above those who depend on him.

There is a cost to this approach, obviously. It disqualifies some smart, dedicated and able people merely because they suffer a single flaw -- and one that apparently is pretty common among the politically ambitious.

But so what? A talented executive can expect to lose her position for a single act of embezzlement. An outstanding journalist may be banished from his profession for one incident of plagiarism.

Of course, those lapses bear directly on how the offenders do their jobs, which is not the case with a governor who strays. But we don't vote for CEOs or newspaper reporters, which means they don't embody our higher aspirations. Americans think those elected to positions of public trust should have enough regard for the public to conduct themselves in an honest, upright way even in matters unrelated to their official duties.

Is it naive of us to believe that a politician who keeps his commitments to his wife will also keep his commitments to us? Probably. But not as naive as thinking that if he betrays her, he'll treat us any better.