South Carolina Gov. Mark Sanford and his family are in the midst of an emotionally wrenching and deeply personal crisis. I feel sorry for them.

I'm willing to grant elected officials — including those who hold the highest office, the presidency — a zone of privacy, as long as their personal peccadilloes don't interfere with the public's business. (Sanford seems to have violated that standard when he flew off to Argentina, secretly, without formally turning the state's business over to the lieutenant governor.) I don't expect politicians to be priests.

Among some constituencies, there is the naive view that a person's fitness for public office can be ascertained in his or her marital fidelity. But that simply isn't so. Life is too difficult and complex for such judgements.

Franklin Roosevelt, deemed one of the nation's best presidents, carried on a years-long affair with Lucy Mercer. By contrast, Richard Nixon is believed to have been the very soul of marital propriety, but he raped the Constitution.

Still, if politicians are going to get a zone of privacy and the respect accorded to full-grown adults, then they must be willing to offer that to others. Those who live in glass houses, etc., etc.

Unfortunately, Sanford belongs to that cadre of politicians, mostly hard-core Republicans, who have been unwilling to stay out of other folks' personal business. That group includes Sen. John Ensign (R-Nev.), who admitted adultery earlier this month. Like Ensign, Sanford opposes same-sex marriage, which opponents claim would undermine heterosexual marriage. (Did gay couples have something to with Sanford's infidelity?)

Like Ensign, Sanford was a harsh critic of former President Bill Clinton. Then a congressman, Sanford called Clinton's conduct with Monica Lewinsky "reprehensible" and insisted that Clinton resign. He voted for impeachment, citing the need for "moral legitimacy."

Actually, I agree that Clinton's conduct was reprehensible. But Sanford joined with his GOP colleagues in making Clinton's reckless behavior a national crisis by pushing impeachment, which distracted from far more important matters. While the president's personal behavior was appalling, it didn't affect the public's business.

And that's where the line should be drawn: Does the private behavior impinge on public performance? Does it jeopardize state affairs?

Jim McGreevey, former Democratic governor of New Jersey, was right to resign because his behavior was well over the line. McGreevy's public sin lay not in his same-sex love affair — that's a personal matter — but in putting his spectacularly unqualified lover on the public payroll.

Eliot Spitzer, former Democratic governor of New York, needed to go because he not only hired a prostitute, an illegal act, but he had also prosecuted prostitution as the state's attorney general. That level of hypocrisy could hardly be tolerated.

Mark Foley, former GOP congressman from Florida, resigned after he was caught sending sexually suggestive e-mails to teenagers serving as congressional pages. Never mind that the middle-aged Foley was chasing young men. He deserved to be kicked out of office for inappropriate contact with youngsters, no matter their gender.

Issuing an abject apology last week, Sanford said he had resigned as head of the Republican Governors Association. He has likely put an end to any presidential aspirations, and he's imperiled his governorship, as well.

But he may have learned a valuable lesson (besides the pain caused by adultery): stay out of other folks' private business. You've got enough to manage.

Cynthia Tucker, an Opinion columnist, writes Sundays and Wednesdays. Reach her at cynthia@ajc.com.