New York City Mayor Bill de Blasio has spent the past few weeks considering a run for the Democratic nomination for president. Thursday morning he finally confirmed that he is indeed running. Or to put it another way, Bill de Blasio is a white male Democratic politician with a pulse.

Only 57 percent of Democratic voters are white, and a majority of them are women. Yet somehow there are only two women of color running for the nomination (Kamala Harris and Tulsi Gabbard) in a field of 22 or 23 serious candidates, depending on how you count them and what your definition of "serious" is. Meanwhile there's Beto, Bennett, Biden, Bullock, Buttigieg, Delaney, Gravel, Hickenlooper, Inslee, Moulton, Sanders, Swalwell — you can't spit in Iowa without hitting some white guy you've probably never heard of wearing a suit and begging to shake your hand.

You can't spit in Iowa without hitting some white guy you've probably never heard of wearing a suit and begging to shake your hand.

In 2018, nonincumbent Democratic nominees were 48 percent women, a huge jump over previous election cycles. Women won 65 percent of primaries against men, according to 538.com, suggesting that Democrats — who, again, are majority women — were showing a decided gender preference. The result was the largest group of elected congresswoman in history, including a record-breaking number of black women, and the first two Muslim women ever elected to Congress. For lower office, Democrats have embraced diversity. Why is the presidential race still so different?

There are three reasons the presidential field has white guys stacked upon it like cordwood: history, entitlement and prejudice.

Though the current Democratic Party at large may favor female nominees, its past tilts in favor of white men. Donald Trump notwithstanding, serious candidates usually run for president only after holding other offices; it's a career endpoint. Democratic voters are more ready to vote for women and people of color now than they've ever been before, in part because the Democratic electorate is less white and less male than ever before. But the Democratic electorate of the past elected many of the people who now have the experience and the status voters typically look for in a presidential candidate. And that older Democratic electorate wasn't as diverse, nor as interested in electing diverse candidates.

The leading Democratic contenders, Joe Biden and Bernie Sanders, started their careers in the 1970s, at a time when women were still rarely elected to higher office. There are still only 25 women serving in the U.S. Senate to 75 men — and only 10 African American senators have served in the entire history of the body. Several of those current senators who aren't white guys are running — Kamala Harris, Amy Klobuchar, Elizabeth Warren, Cory Booker and Kirsten Gillibrand. But this just underlines how important the Senate is as a launching pad for women and people of color.

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If women and people of color feel that they need Senate bona fides to make the leap to the presidential field, though, many men don't seem so constrained. No president in modern history has vaulted into the office without qualifications beyond the House of Representatives, but that hasn't deterred Beto O'Rourke, Seth Moulton, Eric Swalwell or John Delaney (or to be fair, Tulsi Gabbard) from trying. Pete Buttigieg is the mayor of South Bend, Indiana, a city with a population of just over 102,000 people. Mayors and former mayors of New York City, like Rudy Giuliani and Michael Bloomberg, always have presidential ambitions but haven't done so well if they act on this ambitions. Bill de Blasio's approval ratings are especially dismal. And yet, he's going to try anyway.

NY Post greets de Blasio bid: pic.twitter.com/BOLazL2bWA — Michael Calderone (@mlcalderone) May 16, 2019

Ambition is par for the course for anyone in political office. All politicians are motivated by the single burning question, "Why not me?" And with his approval stuck in the low 40s, Trump looks beatable. Analyst Nate Silver estimates that de Blasio could be the 14th or 15th most likely person to win the Democratic nomination. So in some sense, it's natural for de Blasio to want to try. He doesn't bring anything special to the table in terms of policy, vision or skills. But on the other hand, someone has to win. Why not him?

So in some sense, it's natural for de Blasio to try. He doesn't bring anything special to the table in terms of policy, vision, or skills. But on the other hand, someone has to win.

Warren, Gillibrand, Harris and Gabbard are asking "why not me," too. But the threshold for "why not" tends to be lower for men. Research by political scientists Jennifer Lawless and Richard Fox found that women actually become less confident about their qualifications for office as they move from high school to college, while men become more confident. Adult men eligible for officer were 60 percent more likely than women to see themselves as very qualified to run, according to Lawless and Fox. Women were 50 percent more likely than men to think they were not qualified.

A big part of the reason for men's greater confidence is greater encouragement, according to the study authors. Parents are more likely to encourage men to go into politics. So are relatives, friends, religious leaders — basically everyone pushes men to run for office more than women. People have told men like Seth Moulton and Beto O’Rourke and Bill de Blasio that they were what their constituents needed, and that they could win. And so those male candidates figure now, in 2020, that they're what the country needs, and that they can win.

The last reason that white guys dominate the 2020 Democratic field is that prejudice persists. Buttigieg — who, being gay, has faced his own set of barriers — noted, "I do think it’s simply harder for candidates of color or for female candidates." Media coverage of women has tended to focus more on appearance, and women who seek power have been criticized for being ambitious or cold. "When men are ambitious and make savvy political moves, they’re admired. When women do the same thing, they’re admonished," Laura McGann writes at Vox. That can lead women to be more hesitant to run. Certainly, a female mayor of a city the size of South Bend could reasonably assume her candidacy would be treated much differently than Buttigieg’s.

At the end of the day, all presidents except one have been white men. "White man" is still seen as the most natural identity for leaders by the media, pundits, parties and by candidates themselves. That's a big part of why when Bill de Blasio looks in the mirror and sees a white guy, he thinks, "president." After all, why not him?