WASHINGTON, DC - APRIL 11: The Martin Luther King memorial is visible through cherry blossoms at peak bloom around the Tidal Basin on April, 11, 2014 in Washington, DC. ( (Bill O'Leary/Washington Post)

Beverly Gage, a Yale historian, was researching a biography of J. Edgar Hoover in the National Archives when she came across the infamous letter the FBI had written to Martin Luther King Jr., outlining in the crudest form his extramarital escapades and suggesting, King concluded, that he kill himself: “There is only one thing left for you to do. You know what it is.” King did nothing, but the FBI acted. It leaked its dirt to the press.

The year was 1964, and King was already becoming a heroic American figure. Later in the year he would become the youngest person to win the Nobel Peace Prize and, if you will pardon a personal note, it was around that time that I met him — at a news conference in New York at which I flatly knew I was in the presence of greatness. The attempt to sully King’s reputation is one of the FBI’s unforgivable sins.

I did not know at the time about King’s affairs. I learned about them later, once the FBI bugs of King’s home and hotel rooms had become common knowledge in newsrooms around the country. But here’s the thing: No one printed a word of it. I know of no item in a gossip column and, since celebrity TV junk was still in the future, nothing on the air either. Lots of people knew the secret, but the press in those days respected the privacy of public figures: King was saved from ignominy. He was preserved for greatness.

It just so happens that Gage’s account of how she stumbled upon an uncensored version of the letter appeared in the New York Times as I was reading Matt Bai’s recapitulation of the fall of Gary Hart. Bai’s book, “All the Truth Is Out,” is a captivating retelling of how Hart’s presidential aspirations were ended when the Miami Herald staked out his Washington townhouse and wrote that he spent time with a woman who was not his wife. It was a dreadful piece of journalism, until then usually the work of shiny-suited private investigators and not budding Walter Lippmanns — or Cronkites, for that matter.

Bai’s thesis is that journalism — indeed, American culture — turned a corner back in 1987 when reporters, obsessed about character, went poking into the private lives of political figures. I think he has a point, because it has always been clear to me that, whatever character is, it has precious little to do with one’s sex life. Richard Nixon is exhibit A. As far as we know, he never cheated on his wife — merely on the country. Other examples are easy to find. Franklin Roosevelt died with his one-time mistress in the room; John F. Kennedy and Lyndon Johnson were peripatetic womanizers; Thomas Jefferson almost certainly had an affair with his slave Sally Hemings; and his archrival, Alexander Hamilton, was always true to his country but not always to his wife.

Yet the press goes on and on about character, sometimes no doubt as an excuse to expose the salacious — 6 trillion hits! Trending! Eight billion followers! — and sometimes out of a touching naivete about human nature. The damage is not insignificant. Hart, a worthy presidential candidate and a man of high purpose, became a TV punch line. Other politicians suffered similarly — some because their behavior was outrageous (Anthony Weiner comes to mind) but some only on account of prosaic extramarital affairs. (Bill Clinton is in every category imaginable.)

I can’t help wondering what would have happened if King had been exposed at the time. The cries of hypocrisy would have blighted the sun — a minister, a civil rights leader, a married man, a father. Imagine the scene today: The folks at Fox News would have drooled all over the set. The Internet would be aflame, and MSNBC would line up three experts to discuss infidelity until they drained sex of all interest. CNN would try to weave it in with that missing Malaysian airplane.

The result would be the hideous destruction of a great man — and a moral rebuff to one of the greatest of all moral movements, the one that King himself led. A man of immense dignity and incomparable bravery who embodied what is best about America would have been soiled. The vicious FBI letter — it should be framed and displayed in the lobby of the FBI Building — and an accompanying audio tape had failed to do the job intended. Thank God no reporters staked out King as they later did Hart. That, too, was a question of character.

Read more from Richard Cohen’s archive.