Greg Bloom, 33, in rear, works at a table in Big Bear Cafe in the District’s Bloomingdale area on Feb. 19. Younger voters’ numbers have risen in Washington neighborhoods such as Bloomingdale, Shaw, Columbia Heights and the 14th Street corridor. (Andrew Harnik/For The Washington Post)

A surge of young, mainly white voters living in newly affluent neighborhoods emerged as a powerful force in last November’s elections in the District, a seismic shift that mirrors the evolution of the city’s population and could reshape its politics in years to come.

For the first time in 40 years, voters between the ages of 25 and 34 outnumbered senior citizens, an analysis of election data shows. Also for the first time, African Americans, who historically have exerted the greatest influence over District politics, lost their majority among voters.

The young voters cast ballots in gentrifying neighborhoods such as NoMa (short for North of Massachusetts Avenue), the H Street corridor and Shaw, while turnout declined in working- and middle-class African American precincts east of the Anacostia River. The shift appears to have been a key to the overwhelming passage of a ballot initiative to legalize marijuana that took effect last month.

For decades, African Americans defined the nation’s capital, their majority population infusing the city’s neighborhoods, culture and politics. In local elections, black voters powered the victories of mayors such as Marion Barry and Vincent C. Gray.

But in recent years, the city’s population exploded — and blacks lost their majority status. Younger, more affluent residents moved into neighborhoods at the city’s core and became involved in politics and local issues.

D.C. passed two election milestones in 2014

What remains uncertain is whether the marijuana referendum drew residents who are unlikely to participate regularly in politics — or whether a new electorate is taking shape that will alter the future of city politics.

Overall, according to a Washington Post analysis, younger voters accounted for 22 percent of the electorate in November, surpassing seniors, who comprised 20 percent. About 40,000 voters between the ages of 25 and 34 cast ballots, or twice the number turning out in 2010.

While Board of Elections records do not identify voters’ race, the Post based its analysis on neighborhood census data and precinct-by-precinct votes.

Historically black neighborhoods on the city’s eastern side comprised a smaller portion of the electorate in 2014, the Post’s analysis found. At the same time, the percentage of voters grew in neighborhoods rife with new luxury development, such as Bloomingdale and Columbia Heights.

The Post’s analysis found that the registration of voters between ages 25 and 34 grew by nearly 30 percent between 2010 and 2014, and turnout among those voters at least doubled and sometimes tripled in gentrifying neighborhoods.

Nearly 60 percent of those younger voters are nonblack, according to the Post analysis: a mix of whites, Asians and Latinos.

A center of the surge was NoMa, where, in one precinct, the number of votes nearly tripled, from 324 in 2010 to 913 in 2014. The voter tally in a precinct along the U Street corridor — another area in which there has been an infusion of new residents — more than doubled in that time. The same was true in Adams Morgan.

Pedestrians make their way along 14th Street in Washington on Feb. 19. (Andrew Harnik/For The Washington Post)

The new voters include Scott Habrun, 29, a grant writer who moved to NoMa from Ohio two years ago. Habrun said he felt compelled to register to vote mainly because of the pot initiative.

In the process, Habrun also found himself becoming aware of the mayoral candidates, voting for Muriel E. Bowser because “she was in touch with the population more.”

“Everywhere I went, I ran into the candidates,” he said. “They were at every street festival.”

Other newly registered young voters said no single issue motivated them. Instead, they said, participating in the election was an extension of their commitment to the city.

“It was out of a sense of civic duty,” said Stephanie Szurek, 30, a meeting planner who moved from Minnesota in 2011 and lives in NoMa. “This is where our voices can be heard.”

The sharpest declines in voter turnout occurred in African American neighborhoods in Ward 7, east of the Anacostia River, which formed a crucial bedrock of support for Barry and Gray. While young voters migrate to neighborhoods defined by new restaurants and other amenities, black residents in long-established areas complain that the development boom has not reached them.

“People are losing faith in the leadership,” said Gary Butler, a Ward 7 community leader explaining the drop-off in voting. “There’s no one making them want to go to the polls. They’re thinking it’s business as usual.

“We’re getting the same people doing the same things all the time,” he said. “People are burnt out and frustrated.”

Black influence wanes

In the decades after the Civil Rights movement, the nation’s capital was a symbol of African American empowerment. Blacks dominated the city’s culture, government and neighborhoods such as those straddling major thoroughfares like U Street NW and H Street NE.

During political campaigns, candidates focused their appeals on issues important to African American voters, many of them retired local and federal workers who had been ever reliable on Election Day.

The turnout statistics from last November, if sustained, suggest that the formula for political success in the city could change. Chuck Thies, who managed Gray’s unsuccessful 2014 reelection bid, said younger voters represent “an enormous opportunity” for candidates to “tap into a new part of the electorate.”

“The emergence of a new, potentially powerful voting bloc challenges the dominance of the African American voting bloc,” Thies said. “Not that you can ignore the African American base. But a candidate can surely cobble together a coalition that doesn’t depend on the traditional stronghold of older African Americans.”

Among older African Americans, the District’s transformation has enhanced the sense that their importance has been diminished, particularly within the city’s power structure. A majority of the D.C. Council is now white. The recent death of Barry, once a symbol of black prominence in Washington, was another sign of a changed city.

Yet, whether the electoral shifts are fleeting or indicate deeper change is a puzzle that will be answered only in future election cycles.

Josh Mantell, 29, a policy analyst for an environmental organization, said he registered to vote after buying a condominium in Shaw, a neighborhood that has been remade by an influx of young professionals.

No particular issue drove his newfound interest in local politics, although he expressed discomfort with the city’s history of corruption. “It was about settling down,” he said. “When I bought the condo, it was time to commit to D.C. and register. Before that, I was just flirting with the city.”

Matt Maskell, 28, the manager of a hair salon who moved to the District in 2013, said his interest in local issues was driven in part by the city’s thriving gay community and the mayoral campaign of David Catania, who is openly gay.

But he also is following local politics because he plans to remain in the city and open businesses. “I expect to be a regular participant going forward,” he said. “I see this as home for the long haul.”

Young voters are drawing the attention of the city’s political class.

“People need to be polling to find out what these voters are thinking,” said Bill Lightfoot, who was chairman of Bowser’s mayoral campaign. “Find out what their issues are. Find out if you need a message that resonates with them but is different than [for] other voters.”

The Post’s analysis found that blacks still were the majority of registered voters in 2014. But they no longer accounted for most of those who turned out in either the Democratic primary or the general election, in which Bowser defeated Catania.

“We live in an era where you must engage in coalition politics,” said Ron Lester, a longtime Democratic pollster. “All candidates will have to have an agenda that includes the issues that the new voters care about.”

In a number of cases, he said, new voters and older Washingtonians share practical concerns, such as crime and the quality of city services and public schools. “They are different in education, income and race,” Lester said. “But in many ways, they have more in common than you might think.’’

The coalition tradition

Mayoral candidates in the District have assembled coalitions in the past. Barry, for example, won not only black votes, but also white support on the city’s west side when he first won the mayoralty in 1978. Anthony A. Williams captured City Hall in 1998 with support from whites and African Americans, as did Adrian M. Fenty in 2006.

Yet black candidates also have been able to win by pouring resources into the city’s African American neighborhoods, as Barry demonstrated in three successful mayoral races after his first election. When he defeated Fenty in 2010, Gray relied almost entirely on support from black voters.

Bowser, in her campaign, touted herself as a bridge between newer District residents and those whose ties to the District go back generations. During the Democratic primary, when she defeated Gray, Bowser won with support in predominantly white precincts. In the general election, when she beat Catania, who is white, Bowser won with support in African American neighborhoods.

But Bowser did not excite some black voters; turnout in African American neighborhoods declined in November.

“I was struggling to get people to vote who are disgusted with the political system,” said David Smith, a community leader in Ward 7’s Deanwood neighborhood, which is east of the Anacostia River. “People aren’t dumb. The same old, same old isn’t going to work anymore.”

At the same time, voters turned out in greater numbers in gentrifying neighborhoods.

Council member Jack Evans (D-Ward 2) said he sought the support of younger voters during his losing mayoral campaign last year, attending meet-and-greets at downtown technology firms and start-up companies. But he lamented that they were not moved to vote for him.

Ethan Spaner, 29, is a policy adviser at a not-for-profit organization who moved from Brooklyn to the H Street corridor two years ago. He registered on Election Day.

“When I moved to D.C., I didn’t think I’d be here that long,” he said. “A year and a half later, I’m still here. It was a way to take ownership of the city.”