CONCORD, N.H. — The Democratic Party's nomination campaign began with the biggest and most diverse field in history. More women and more candidates of color populated the field than ever before. Unless something changes quickly, the contest could devolve into a competition among only white men.

Despite having two women and an Asian American sharing the stage at Friday night’s debate in New Hampshire, right now the Democratic race appears to be a contest among two white men in their late 70s, Sen. Bernie Sanders (I-Vt.) and former vice president Joe Biden, and another in his late 30s, former South Bend, Ind., mayor Pete Buttigieg. Another septuagenarian, former New York mayor Mike Bloomberg, is waiting to pounce, depending on the results of the first four primaries and caucuses.

The fact that this is a battle among white men represents an unexpected turn for a party whose success in the 2018 midterms depended heavily on an outpouring of support and activism by women and whose failure in 2016 was the result, in part at least, of a falloff in turnout among voters of color, especially African Americans. The party’s future depends on both those groups and, overlapping with them, the active support of younger people.

The changing face of the Democratic Party is an oft-told story, celebrated by party leaders and by rank-and-file Democrats alike. It is a point of pride for Democrats that their party looks more like the changing American population than does the Republican Party, whose presidential candidates of late have gotten about nine of every 10 votes from whites.

What has gotten less attention is the tension the diversification of the Democratic coalition has produced under the party’s big tent. The rising parts of the population are the rising parts of the Democratic Party. They now want more than acknowledgment that their votes are important. They are not satisfied simply to cast their votes for a Democratic candidate. They want a bigger voice at the Democratic table.

Much has been said about the ideological divisions within the party, highlighted again during Friday’s debate at Saint Anselm College in New Hampshire by questions about whether Sanders’s brand of democratic socialism would sink him in a general election against President Trump and take down other Democrats in Senate and House races or produce big turnout among a new coalition of voters.

Debates over whether Medicare-for-all amounts to a budget-busting, complex, big-government idea or the obvious and essential health-care future for a country where many people have no insurance or are saddled with high deductibles and other costs. Conflicts like that are among the choices Democratic voters will be weighing in the primaries and caucuses.

But there’s another division that the party is struggling to resolve, which is who has power and who should have power.

More than a year ago pollster Anna Greenberg, looking ahead to 2020 and beyond, played down the ideological divisions among Democrats, but she made another important observation. She described Democrats as “a party in flux” not over ideology but over that balance of power within the party’s coalition.

Greenberg said she saw the coming period as “the last gasp of older white men who have control in the party.”

The 2020 campaign was to be the moment when the rising coalition asserted and perhaps took power, but it has not worked out that way so far. There’s no single reason that has turned out to be the case. Some people blame it on the fact that the first two states to vote, Iowa and New Hampshire, are predominantly white. Some blame it on the inability of candidates who have fallen to the sidelines to run better campaigns.

Three candidates of color — entrepreneur Andrew Yang, Rep. Tulsi Gabbard (Hawaii) and former Massachusetts governor Deval Patrick — remain as active but lagging candidates. Yang has his Yang Gang and has raised some money, but he does not have enough support to be a serious contender. Gabbard launched her campaign last February and Patrick jumped into the race late, but neither has yet to make a mark.

But gone from the field are two black senators, Kamala D. Harris (Calif.) and Cory Booker (N.J.), and the Latino former housing secretary Julián Castro. All entered the race with serious expectations. Harris became one of the most talked-about candidates in the early stages. But none of them, ultimately, was able to attract serious support or serious amounts of money.

In addition to Gabbard, two other women remain — Sens. Elizabeth Warren (Mass.) and Amy Klobuchar (Minn.). While Gabbard has been a gadfly in the race, Warren and Klobuchar have played more significant roles. Gone among the female candidates are Sen. Kirsten Gillibrand (N.Y.) and author Marianne Williamson.

Warren entered the campaign as one of the three best-known and best-regarded candidates, along with Biden and Sanders. She set the pace with a flurry of plans for attacking corruption in government and concentrated power in the private sector. She led the field in Iowa at one point, but last Monday she finished a weak third in Iowa and appears to be struggling in New Hampshire.

Klobuchar has struggled from the start to break into the upper ranks, overshadowed by better-funded candidates and trying to make her mark as a moderate, results-oriented Democrat in a party that has been moving to the left. “If you are tired of the extremes in our politics and the noise and the nonsense, you have a home with me,” she said Friday night.

At Friday’s debate, Warren was a quiet presence, staying out of the scrums for the most part and focusing on the message that has guided her candidacy while trying to present herself as someone who can unite the party. If that strategy doesn’t give her a boost, she will have difficulty overtaking the leaders here.

Klobuchar had what might be the best night of her campaign, witty and sharp-tongued at the same time. She questioned whether Sanders could effectively lead the party in a general election, and she accused Buttigieg of taking the easy path by highlighting his outsider status and implicitly criticizing people with Washington experience.

“It’s popular to say and makes you look like a cool newcomer,” she said to the 38-year-old mayor. “I don’t think that’s what people want right now. We have a newcomer in the White House and look where it got us. I think having some experience is a good thing.”

But she’s had good debate performances before, and they’ve never translated into growth in support. She has remained in single digits in national polls and ended up fifth in Iowa. She hopes for better in New Hampshire but has to rise quickly to become a force in the nomination contest.

For many female voters and for many voters of color, this turn in the race has produced frustration and a feeling of being left out once again and a step down from when the campaign started a year ago.