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. Donald Trump’s philandering was long fodder for the tabloids.
Bill Clinton's affair with Monica Lewinsky became very well known while he was in the White House. 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. These episodes were known in the Clinton circle as “bimbo eruptions,” a term that did credit to neither Clinton nor his partners. But they antedated his presidency, and those who voted him into office in 1992 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. It took place while Clinton was in the White House—and it took place mostly in the White House. 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. (Whether Clinton’s decision to liaise with Lewinsky was a matter of the heart is open to doubt.) But when you’re president, personal decisions become political decisions. 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. When the story became public, Clinton denied having a sexual affair with Lewinsky.
It's not a crime for presidents to lie in public. It might be a sin, and it might be a mistake, but it's not a crime. Lying under oath in a legal proceeding is another issue. In a civil case brought by Paula Jones regarding an earlier affair with Clinton, he denied having sex with Lewinsky. He denied it again in testimony before a grand jury summoned to consider whether he had perjured himself in the Jones case.
At this point Congress stepped in. The House of Representatives voted to impeach Clinton, and his case went to trial in the Senate.
Clinton still denied having sex with Lewinsky and consequently having lied about it. But his denial depended on a narrow definition of sex, one that excluded oral sex.
The prosecution in the Senate trial insisted that Clinton's impeachable “high crime"—with “misdemeanor,” the undefined constitutional standard for removal from office—was not sex, whether oral or otherwise, but perjury and accompanying obstruction of justice. Clinton counsel Dale Bumpers rejoined, “H. L. Mencken said one time, ‘When you hear somebody say this is not about money, it's about money.’ And when you hear somebody say this is not about sex, it's about sex.’”
The Senate seemed to agree with Bumpers, and it concluded that Clinton should not be removed from office for his affair with Lewinsky. Conviction requires a two-thirds majority. On neither of the two counts of the impeachment charge did the prosecution get even a simple majority.
Clinton remained in office. But some of his most devoted supporters cursed him under their breath. They resented not the affair with Lewinsky but the loss of momentum the scandal caused in Clinton's presidency. They’d voted for him believing he had the charisma and the opportunity to make a significant change for the better in American life. He wasted that charisma on a twenty-something intern and in doing so squandered the opportunity. That was Clinton’s high crime, whether impeachable or not.
I put a good deal of blame on Clinton for Gore's loss to Bush as well, part of the "momentum" thing perhaps.