Yes, Reagan was the first divorced US president, although Franklin Roosevelt and Florence Harding had both threatened it. (Warren had multiple affairs, including one where his family paid off his partner to keep quiet.) But if you don’t mind, I’ve going to divert into the real story here: Rachel and Andrew Jackson.
In 1787, young Rachel had married a man named Lewis Robards. Lewis was, by all accounts, a horrible person. (Not that Andrew proved to be much better, but roll with it.) According to people who knew him, he beat his wife, broke codes of honor by tsking payoffs instead of duelling, accused her of adultery when he was the one cheating, and raped enslaved women. So perhaps unsurprisingly, in 1791, Rachel and Andrew got married.
If you think there’s a step missing there, you’re right: Rachel and Lewis were probably not divorced when she married Andrew.
Oops.
In fact, if you believe some reports, the story is even better/worse. In 1789, we know, Rachel left Kentucky for Spanish-controlled Mississippi. She was pretty clearly escaping an abusive relationship, since her marriage to Lewis would not be recognized in Spanish territory. Andrew, on the other hand, went along...possibly so they could get married already.
(I must say at this point that Christina Mune and Robert Remini have credited Andrew with a reputation as a "defender of women" for this. To be clear: he supported genocidal policies against Native Americans and enslavement of black Americans; he was no "defender of women.")
Yes, there are mitigating legal circumstances. Lewis had filed for divorce in 1791. And Rachel and Andrew’s second wedding, in 1794, probably reflects their belated realization that their first marriage wasn’t valid because the divorce wasn’t final until 1793, and a desire to do things right. And more to the point, as Patricia Brady and Paul Boller observe, this sort of semi-informal “frontier marriage” and "frontier divorce" was not entirely unusual in the late 18th century.
But there’s still that small problem of Andrew being a lawyer who absolutely knew what he was doing and had the connections, money, and travel ability to do it a different way.
Rachel's family (the Donelsons) being rather prominent and divorce notices needing to be published in the newspapers, the timing of the Jacksons' marriage was not exactly a secret. And as Andrew's political career picked up...steam...before this idiom would make sense...his cuckolding of Lewis became quite the target of political attacks. Naturally, he responded like any proper gentlemen: started challenging his political opponents to duels.
During the 1820s, gearing up for the ultimate challenge of presidential campaigning, the long-ago divorce/marriage/timing fuzziness became a major target for Jackson's opponents to argue that he was morally unfit to be president. (This was true, but not for the reasons promulgated in the press.)
Naturally, much of the abuse was actually directed first and foremost at Rachel--only secondarily at Andrew, for consorting with the type of woman who would do such a thing.
Charles Hammond is among the best/worst here. In his pamphlet View of General Jackson's Domestic Relations, in Reference to his Fitness for the Presidency--whose title probably says everything--he attacks Rachel for being immoral in about twelve different ways, attacks Andrew's defense of her as immoral and insufficient to exonerate her...then praises Rachel for pristine conduct while married to Andrew and attacks Andrew for not defending his pristine wife against said accusations.
Or take Thomas Arnold:
Anyone approving of Andrew Jackson must therefore declare in favor of the philosophy that any man wanting another man's pretty wife has nothing to do but take his pistol in one hand and a horsewhip in the other and possess her.
Or fancy learning to write your ABCs:
The Adultress. The Bully. The Cuckold.
Unfortunately for the country, none of this was enough to prevent Andrew’s election.
Unfortunately for Rachel, she had to endure all this abuse in the media--and then died between election day and Andrew's inauguration. Contemporary sources, sympathetic to Rachel, even attribute the stress from the smear campaign to hastening her death. Unfortunately, Rachel's own papers have been lost (mostly to a fire), so we don't have her voice from the campaign years or the period leading up to her death. But it's not hard to see her last months as unhappy ones.
..But fortunately for the media, President Andrew Jackson wasn't finished producing scandals related to women.
Which would end up as a whole other disaster for the U.S., in the end. But I'm already on a tangent here, and so that is a story for a different thread.
This came up in passing on the r/askhistorians podcast episode on pot. Most of the focus was on Nancy, as she had noticeably (re?)married up, which played into decision to join in on a growing anti-marijuana movement as a defining issue.
First, for the sake of historical completeness, Ronald Reagan and Donald Trump are the only divorced presidents. The only other divorced major-party nominees were Adlai Stevenson (Democrats, 1952 & 1956), Bob Dole (Republicans, 1996), John Kerry (Democrats, 2004), and John McCain (Republicans, 2008). Stevenson was the only one of those who had not remarried.
This doesn't directly answer the Reagan question, but it's interesting to compare his situation to that of the only divorced vice-president, Nelson Rockefeller. Rockefeller was one of the most prominent figures in the liberal wing of the Republican Party in the 1960s. While serving as governor of New York, he separated from and not long after divorced his wife of over 30 years, Mary, with whom he'd had five children (one had died by then). Nelson kept the lower floor of their three-floor penthouse apartment in New York City; Mary and the children lived on the upper two floors.
Just over a year later, in May 1963, he married a former aide who was 20 years younger than him, Margaretta "Happy" Filter, who had four children of her own and whose own divorce had only been granted five weeks earlier. They had a son in 1964 and another in 1967.
At the time, Rockefeller was considered a leading candidate for the 1964 Republican presidential nomination. The party was in the midst of a schism between its more moderate-to-liberal members, led by Rockefeller and others like Michigan Governor George Romney on the one side, and more conservative members like Arizona Senator Barry Goldwater on the other. It's hard to say how much Rockefeller's divorce and remarriage contributed to his losing the nomination to Goldwater, but it was certainly a factor.
For example, former Connecticut Senator Prescott Bush remarked, "Have we come to the point where a governor can desert his wife and children, and persuade a young woman to abandon her four children and husband? Have we come to the point where one of the two great parties will confer its greatest honor on such a one? I venture to hope not." (In fact, Happy later lost a custody battle over her children.) Notably, Prescott Bush was the father of Ronald Reagan's running mate, George H.W. Bush.
A news story from shortly after the marriage (May 3, 1963) surveyed party leaders from around the country, and reaction was mixed. A few said it would not be a big deal, but several were adamant otherwise. William Roth of Delaware said there was "no question in my mind but it has hurt him, at least temporarily." New Jersey Republicans indicated the marriage "would deprive the Governor of any chance of wining the nomination and defeating Mr. Kennedy." Richard Kleindienst of Arizona said that the marriage would make Rockefeller "a less desirable candidate." Some state leaders would not comment for the record, but one from Michigan said "I think it would hurt him. The rapidity of it all -- he gets a divorce, she gets a divorce -- and the indication of the break-up of two homes. Our country doesn't like broken homes."
Contemporary news reports suggest that the issue dogged Rockefeller in the months leading up to the 1964 convention. A New York Times story from March of that year is headlined "Rockefeller Advisers Urging Him To Make Statement on Divorce," and notes that "[a] number of observers, both in and out of the Governor's organization, are convinced that his remarriage was the basic cause of his third‐place showing in the New Hampshire primary." Happy Rockefeller's obituary said that the couple was compared at the time to King Edward VIII of England and Wallis Simpson, the divorcee he abdicated the throne to marry. That obit quotes a story about the polls back then: "Only a few weeks ago Gov. Nelson A. Rockefeller was far out in front. Now, abruptly, the picture has changed. The Rockefeller image has been damaged."
Rockefeller sought the Republican nomination again in 1968, but the mood of the party had shifted, and it's difficult to say whether he would have won over Richard Nixon even without the divorce baggage.
In 1974, Nixon resigned the presidency, and his vice-president, Gerald Ford, assumed the office. Under the 25th Amendment to the U.S. Constitution, Ford nominated Rockefeller as the new vice-president, and he was confirmed by Congress (although not unanimously; Goldwater's was one of the votes against him). Again, divisions in the Republican Party and the ascendancy of its more conservative wing led to pressures against Ford and Rockefeller. In the lead-up to the 1976 election, Ford dropped Rockefeller from the ticket and chose Kansas Senator Bob Dole as his new running mate. Interestingly, Dole himself was divorced in 1972 and remarried in 1975.
Rockefeller died in 1979 at age 70. He had a heart attack in the home of a 25-year-old staffer, and speculation has long persisted over whether the two were having an affair.
So, to bring this back to Reagan, it's possible that the mere fact that Rockefeller had been "a heartbeat away" from the presidency as a divorced man had simply broken any taboo over the matter by the time Reagan was nominated. It's also worth noting the contrasts between their situations as reasons for why Rockefeller's was more problematic. First, Rockefeller was in office and actively seeking the presidential nomination during his divorce and remarriage, while Reagan was not in politics yet when he divorced and remarried. Second, Rockefeller's personal issues were much more recent, whereas Reagan had been remarried for over 25 years before he became president (and even 15 years before he became governor of California). Third, the age difference and involvement of children in the Rockefeller situation made it more unseemly to some; see the Bush quote above about Rockefeller breaking up two families. And of course, there was a major cultural shift generally in attitudes towards divorce between 1964 and 1980.
To sum up, Reagan's divorce obviously wasn't a deal-breaker in his quest for the presidency, and while it's hard to say that Rockefeller's divorce was the only thing keeping him from being nominated, it certainly seems to have been a major contributing factor.
Sources: Timothy Noah, book review: "'On His Own Terms: A Life of Nelson Rockefeller,'" by Richard Norton Smith, New York Times, Nov. 14, 2014 https://nyti.ms/116e13C
Eric Pace, "Mary C. Rockefeller, Governor's Former Wife, Dead at 91," New York Times, Apr. 22, 1999 https://www.nytimes.com/1999/04/22/nyregion/mary-c-rockefeller-governor-s-former-wife-dead-at-91.html
Robert D. McFadden, "Happy Rockefeller, 88, Dies; Marriage to Governor Scandalized Voters," New York Times May 19, 2015 https://nyti.ms/1JxEfir
"Rockefeller Advisers Urging Him To Make Statement on Divorce," New York Times Mar. 20, 1964 https://nyti.ms/2LIIJIS
"Mrs. Rockefeller Loses Suit Over Four Children," New York Times Oct. 1, 1964 https://nyti.ms/1XUqBLR
"Rockefellers Expect Baby in Early June," New York Times Jan. 1, 1964 https://nyti.ms/2LFc0nP
"Many in G.O.P. Say Marriage Would Hurt Rockefeller in 1964; Voter Effect Weighed Michigan Reaction," New York Times May 3, 1963 https://nyti.ms/1Ls0WlS