Kate Andersen Brower is a CNN contributor and the author of "First Women: The Grace and Power of America's Modern First Ladies" and "The Residence: Inside the Private World of the White House." This article is adapted, in part, from portions of those books . The opinions expressed here are solely those of the author.

(CNN) A former Playboy model who alleges that she had an affair more than a decade ago with President Donald Trump apologized to Trump's wife, first lady Melania Trump, in an interview Thursday evening. Melania now shares the dubious distinction of being a publicly scorned first lady with one other woman: her husband's 2016 rival for the presidency and sworn enemy, former first lady Hillary Clinton.

Karen McDougal told Anderson Cooper in an exclusive interview on CNN on Thursday night that she'd had a sexual relationship with Donald Trump a decade ago, while Trump was married, and that she was "sorry" for what she had done to Trump's wife, Melania. "What can you say except, I'm sorry?" she said, adding, teary-eyed, "I'm sorry. I wouldn't want it done to me."

The White House has denied the affair allegations, which became public in a Wall Street Journal article before the presidential election; it detailed how the parent company of The National Enquirer had paid for McDougal's story and never published it.

McDougal's apology, coupled with other, very public allegations from adult film star Stormy Daniels -- that she, too, had an affair with Trump -- have thrust the Trumps' marriage into the spotlight in a way we have not seen since the 1990s, when Bill Clinton's affair with White House intern Monica Lewinsky dominated the headlines.

To be sure, many first ladies have had to endure their husband's infidelity, although they were carried out well below the radar. But that was before cable news and social media.

The stories of rampant cheating by Franklin Roosevelt, John Kennedy and others are so legendary that in a 1997 letter Monica Lewinsky sent to Bill Clinton pleading with him to see her, she even referred to Roosevelt's longtime mistress Lucy Mercer. "Oh, and Handsome [Lewinsky's nickname for the president], remember FDR would never have turned down a visit with Lucy Mercer!"

JUST WATCHED Former Playboy model to Melania: I'm sorry Replay More Videos ... MUST WATCH Former Playboy model to Melania: I'm sorry 00:29

Mercer, not Roosevelt's wife Eleanor, was by his side when he died in Warm Springs, Georgia, in 1945. And Jackie Kennedy knew her husband saw other women, but at the time there was a gentlemen's agreement in the press never to reveal it.

Jackie suffered bouts of depression over her husband's philandering and once, when she was giving a reporter friend of hers from Paris Match a tour of the White House, she spotted a woman, whom she suspected was having an affair with her husband, sitting in his trusted secretary Evelyn Lincoln's office. Jackie turned to her friend and said, in French, "This is the girl who supposedly is sleeping with my husband."

But it was not until Hillary Clinton that a first lady would be forced to directly confront such embarrassing and hurtful public allegations of her husband's betrayal. This national -- global, really -- exposure went well beyond the the years of training Clinton possessed as first lady of Arkansas when her husband was governor.

But it is all new for Melania, who does not like the spotlight.

Bill Clinton's proclivities were no secret and were well-known in his inner circle and probably by his wife long before he won the presidency. During the 1992 presidential campaign, Hillary's close friend and adviser Susan Thomases issued a similar warning to the one a friend of JFK's delivered to him 36 years earlier. Thomases said: "You're stupid enough to blow this whole Presidential thing over your d--k. And if that turns out to be true, buddy, I'm going home, and I'm taking people with me."

JUST WATCHED McDougal appears in photo with Trump family Replay More Videos ... MUST WATCH McDougal appears in photo with Trump family 01:45

But Clinton's past came back to haunt him in the White House. As I detailed in a 2016 book I wrote about first ladies, one overnight White House guest of the Clintons remembered hearing the phone ring in the hallway of the second floor residence around midnight. The president picked it up, and after a moment, slumped over and yelled, "Oh s--t," and slammed the phone down. Clinton straightened himself up and continued entertaining his guests well into the early morning hours, as though nothing had happened.

The next morning the house guests -- there were always house guests during the Clinton years -- got up and went to the sunny Solarium, with its floor to ceiling windows overlooking the Washington Monument and the Mall, to have a quiet breakfast. The Washington Post, The New York Times and The Wall Street Journal were laid out on a table and right away they could see what had upset the president: Paula Jones had just filed a formal lawsuit accusing the president of making an unwanted sexual advance toward her when he was Arkansas governor and she worked in his office.

Unlike Jackie, Hillary Clinton had no choice but to address her husband's philandering in a very public way. Like Pat Nixon during Watergate, Hillary Clinton stopped reading the newspapers at the height of the barrage and blamed others, in this case Republicans, for trying to bring down her husband.

"She worked out a resolution that worked for her," Thomases said. "It was important for her to keep their marriage together." Shirley Sagawa, who at different times served as Hillary Clinton's domestic policy adviser and deputy chief of staff when she was first lady, said that Monica Lewinsky was a "terrible distraction" and that members of Hillary's inner circle were all "very angry at the time....It was a very complicated time and she handled it all with such grace."

Inside the walls of the residence, there was deep pain. Hillary had been through this before, even carefully choreographing camera angles during her first "60 Minutes" interview in 1992, when she sat beside her husband, who was asked difficult questions about an alleged 12-year affair he had with Gennifer Flowers.

The biggest headline of the interview was not anything he said, however; it was when she broke from the script and said, "I'm not sitting here, some little woman standing by my man like Tammy Wynette." She had known about his cheating and she wasn't about to let it stand in the way of their chance to win the presidency.

But like the Roosevelts before them, the political partnership and deep mutual affection kept the Clintons together. The same was true for the Kennedys. A week after their 10th wedding anniversary, Jackie wrote a letter to their friend Charley Bartlett, who had fixed them up. She told him she knew Jack would have been happy without being married but, without Jack, her life would have "all been a wasteland, and I would have known it every step of the way."

It remains to be seen if the bond between the Trumps is as strong.