It's not known how many presidents had extramarital affairs while in the White House. It's not even clear what should count as an extramarital affair.
Does it mean outside of marriage, or outside of your marriage? Thomas Jefferson was a widower during his long relationship with Sally Hemings. James Buchanan, the only never-married president, shared living quarters with William Rufus King, prompting speculation then and later of sexual intimacy between the two. Franklin Roosevelt was emotionally intimate with Missy LeHand, his personal secretary, to the annoyance of Eleanor Roosevelt.
Does that count? The dalliances of Warren Harding and John Kennedy were known at the time to insiders. But they weren't confirmed to the broader public until after the deaths of those presidents. But whether it was a sexual relationship depended, at least in Clinton's interpretation, on what counted as sex. Clinton had a history of cheating on Hillary Clinton. But they antedated his presidency, and those who voted him into office in were apparently willing to let bygones be bygones.
To put it differently, if Hillary didn't deem the affairs cause for dumping the cad, Clinton voters wouldn't either. The Lewinsky affair was different. That Lewinsky was a White House intern, a position much sought after by young people, and that Lewinsky was less than half Clinton's age, made it perhaps more predictable and definitely more tawdry.
Presidential decisions are usually not decisions of the heart. If nothing else, foolish or reckless decisions reflect badly on the judgment of the president making them. And that reflection can become public if the story surfaces, as stories involving presidents often do. Clinton's affair with Lewinsky lasted a year and a half. Lewinsky confided it to Linda Tripp, who leaked it to Kenneth Starr, who was investigating Clinton on allegations involving other activities.
