WASHINGTON — One is in a same-sex marriage. Another has never been down the aisle. Others are on second spouses, or in pairings in which the wife is the breadwinner and the husband stays home.

All of them are Democrats running for president, even though none fits the mold of the traditional American family.

"The presidential candidates are finally reflecting the diversity of family life in the country," said Andrew Cherlin, a Johns Hopkins sociologist who studies marriage. "If they seem a bewildering array of families, well, so does the nation."

Barack Obama and Hillary Clinton, who broke precedent in other critical ways as presidential candidates, hewed to traditional marital and parenting roles. But outside the White House, American families have been changing.

Marriage is delayed, cohabitation and divorce are more accepted, as is being single. Children are now slightly more likely to live with a single parent than with married parents where the father works and the mother stays home.

There is no longer a typical American family. And the men and women vying for the Democratic presidential nomination represent almost every permutation of the complicated modern dynamics of the 21st century.

Beto O'Rourke, despite his counterculture past as a hacker and punk rocker, is the only candidate among the eight best-known 2020 Democratic contenders with a "conventional" family — and he got in trouble for joking about it in Iowa, saying his wife was back home raising their three young children "sometimes with my help."

Bernie Sanders embraces his wife Jane O'Meara Sanders after the Vermont delegation cast their votes during roll call on the second day of the Democratic National Convention at the Wells Fargo Center on July 26, 2016 in Philadelphia, Pennsylvania. Chip Somodevilla / Getty Images

There's Sen. Bernie Sanders, I-Vt., who has been married twice and has raised children and stepchildren from multiple relationships, including outside marriage. Sen. Kamala Harris, D-Calif., is part of a mixed-race marriage and didn't tie the knot until she was nearly 50.

"We have a huge, very modern family," Harris told Jimmy Kimmel.

And Sen. Elizabeth Warren, D-Mass., who married and divorced young but kept two children and her last name from that relationship, before settling down with her current husband, who picked up his life to facilitate her career and family.

"Bruce quietly took over most of the cooking," Warren wrote in her memoir of their early lives together.

Sens. Amy Klobuchar, D-Minn., and Kirsten Gillibrand, D-N.Y., are both primary breadwinners in their households, according to their Senate financial disclosures — an uncommon role for women not so long ago.

Sen. Cory Booker, D-N.J., like a growing number of Americans, has never been married (he recently acknowledged that he’s dating the actress Rosario Dawson). And there's Pete Buttigieg, the mayor of South Bend, Indiana, whose husband took his last name and endearingly brags about him on Twitter.

INT. Irish Pub

The two gentleman are sharing a pint on their first date.

Chasten: do you play any instruments?

Peter: the piano and guitar

Chasten: oh neat. ever played in public?

Peter: yeah I played Rhapsody in Blue with the symphony orchestra

Chasten: *spits beer on table* https://t.co/USnPbFz654 — Chasten Buttigieg (@Chas10Buttigieg) March 27, 2019

Former Colorado Gov. John Hickenlooper and Rep. Tulsi Gabbard, D-Hawaii, have both divorced and remarried.

And then, of course, there's President Donald Trump, who has been married three times and had children with each wife.

Families like O'Rourke's, with parents in their first marriage, are now a minority — a far cry from 1960 when they accounted for 73 percent of children's households, according to the Pew Research Center.

The only major family type not represented in the 2020 field is single parents, who now account for about a quarter of all homes where kids are being raised.

Still, the idealized nuclear familiar of the "Leave It to Beaver"-era continues to play an outsize role in the popular imagination, even though that type of family was never as common as thought.

"Marriage is no longer viewed as compulsory," said Susan Brown, the co-director of the National Center for Family and Marriage Research. "It's just one in an array of options.”

As recently as 1964, Nelson Rockefeller's divorce and remarriage scandalized the nation and helped cost him the Republican presidential nomination.

"Have we come to the point where a governor can desert his wife and children ... where one of the two great parties will confer its greatest honor on such a one? I venture to hope not," scoffed former Sen. Prescott Bush, a Connecticut Republican who had been a Rockefeller ally but turned against him after he remarried.

Amy Klobuchar waves to the crowd with her husband John Bessler and daughter Abigail Bessler after announcing her candidacy for the 2020 Democratic presidential nomination in Minneapolis, Minnesota, on Feb. 10, 2019. Eric Miller / Reuters

America has had only two divorced presidents (Ronald Reagan and Donald Trump), even though there's plenty of evidence that many more had affairs.

“Many individuals lived up to the strict standards of the past, but as a system, it was based on pretty systematic hypocrisy," said Stephanie Coontz, a historian of American family life at Evergreen State College in Olympia, Washington. "Now, our values are more in line with our practices."

More than 130 years ago, President Grover Cleveland may have raped one woman and married another whose deceased father had entrusted him to be her legal guardian. He was 49, she was 21. He is the only sitting president to be wed in the White House.

On the other hand, there's James Buchanan, who was ridiculed in his time for being a bachelor, with the New York Times editorial board noting, “Cain was a bachelor and so was Judas Iscariot!” Now, many historians say Buchanan was most likely gay and he's been regarded more warmly for it.

It's a change Buttigieg especially is aware of — even though he said his "gaydar" isn't powerful enough to determine Buchanan's sexuality.

"When it first crossed my mind that I might run for office someday, I believed that coming out would be a death sentence," Buttigieg said when he announced his 2020 run. “So the world is changing but it’s not changing on its own. ... If I can be part of chipping away at that, then that's one more reason to give this a look."