Hillary Rodham Clinton set out 10 months ago to inspire and energize the Democratic Party, hoping to bring together the rising American electorate of black, brown, young and female voters into a durable presidential coalition. But buried beneath Mrs. Clinton’s wide-ranging and commanding victories on Tuesday night were troubling signs of a party that has not yet rallied to her call.
Democratic turnout has fallen drastically since 2008, the last time the party had a contested primary, with roughly three million fewer Democrats voting in the 15 states that held caucuses or primaries through Tuesday, according to unofficial election results. It declined in virtually every state, dropping by roughly 50 percent in states like Minnesota and Texas. In Arkansas, Alabama, and Georgia, the number of Democrats voting decreased by roughly a third.
The fall-off in Democratic primary turnout — which often reveals whether a candidate is exciting voters and attracting them to the polls — reached deeply into some of the core groups of voters Mrs. Clinton must not only win in November, but turn out in large numbers. It stands in sharp contrast to the flood of energized new voters showing up at the polls to vote for Donald J. Trump in the Republican contest.
Some Democrats now worry that Mrs. Clinton will have difficulty matching the surge in new black, Hispanic, and young voters who came to the polls for President Obama in 2008 and 2012.
“Barack Obama without that surge is John Kerry,” said Cornell Belcher, a Democratic pollster who worked on Mr. Obama’s re-election campaign, referring to the losing Democratic nominee in 2004. “Just turning out the traditional minority base is not a 51 percent pathway going into November.”
In three precincts of Virginia’s Third Congressional District, the heart of the state’s African-American community, where overwhelming black turnout in 2008 helped Mr. Obama win the state, turnout was down by an average of almost 30 percent on Tuesday night. The district includes most of Richmond and Petersburg, as well as Newport News and Norfolk, Va.
In Nevada, exit polls suggest that Hispanic voters — who have helped push the once deeply Republican state toward Democrats in national elections — voted in significantly lower numbers than in 2008.
Even Mrs. Clinton’s strong victory in South Carolina, which was celebrated for her dominance among African-American voters, obscured a big decline in black turnout of about 40 percent. In Iowa, where Mrs. Clinton eked out a narrow win after a hotly fought battle last month with Mr. Sanders, exit polls suggested that turnout for voters under the age of 30 dropped by roughly 40 percent from 2008.
The results suggest that Mrs. Clinton, who has outraised every other presidential candidate and has the overwhelming support of her party’s elected leaders, still faces a daunting and difficult road to reassembling the winning Obama coalition.
In interviews, Democrats cited several factors for the low turnout among Democratic voters, including Republican-backed laws that have raised new barriers to voting among minorities and college students and the expectation that Mrs. Clinton was almost certain to be the nominee. Some also blamed the Democratic National Committee’s debate planning: the party’s chairwoman, Debbie Wasserman Schultz, scheduled relatively few debates, several of them on weekends or in competition with major sporting events. The schedule, widely interpreted as an effort by Ms. Schultz to help Mrs. Clinton, instead meant that many Democrats never saw some of the candidates’ most vigorous discussions of racial discrimination, overincarceration and police violence.
“What were they thinking? It’s mind-boggling to me,” said Stefanie Brown James, a Democratic consultant who worked on Mr. Obama’s 2012 campaign. “Some of the onus is on the Democratic Party.”
Some Democrats said they did not believe that turnout in the primaries necessarily foreshadowed problems for the Democratic nominee in the general election, particularly in states that Mr. Sanders did not vigorously contest. Mrs. Clinton’s supporters insist that many Democrats would become more energized as the general election drew nearer, particularly if Republicans nominated Donald J. Trump as their standard-bearer.
In a general election polarized by Mr. Trump’s appeals to the economic and cultural anxieties of white, working-class voters, those Democrats argued, black and Hispanic voters would turn out in strongly to defeat him.
“It is pretty much universally the case that the party out of power sees higher turnout during its nominating contests, but that is not determinative of general election success,” said Brian Fallon, a spokesman for Mrs. Clinton. “In the last three election cycles in which Democrats controlled the White House, Republicans had higher turnout during the primaries, but Democrats went on to win the popular vote.”
But other Democrats are concerned enough that they have begun looking for ways to drive up enthusiasm for the general election.
A new group called Black Votes Matter, led by Democratic strategists based in New York, is trying to raise $25 million for a new effort to identify and energize African-American voters. Charlie King, a former executive director of the New York Democratic Party, said the group would focus on five states where black voters were particularly pivotal for Democrats and where, in some cases, lawmakers had also imposed new voting restrictions in recent years.
“If there is a drop-off in the surge vote in the Florida, Ohio and Virginia, that is 60 electoral votes,” Mr. King said. “No one has captured the real dilemma in the 2016 election. It’s not a question of whether Hillary Clinton would get 90 percent of the black vote. The question is: 90 percent of what?”
Mr. King and other Democrats said that Mr. Trump could present Democrats with the prospect of a greatly altered political and demographic map. His candidacy is helping spur higher turnout in each of the first four Republican contests, including Nevada, where Mr. Trump’s vote total by itself surpassed overall turnout in the 2012 election, setting a state record. On Super Tuesday, Republicans smashed turnout records in Massachusetts, a traditionally Democratic-leaning state, and saw huge turnout in both Virginia and Tennessee.
And despite the seemingly inexorable demographic rise of Hispanic voters, the American electorate is still overwhelmingly white. Some analysts said they believed Mr. Trump could even exceed Mitt Romney’s 59 percent share of the white vote — winning over disaffected Republicans and even working-class Democratic men, and putting Democratic-leaning swing states like Michigan, and potentially Pennsylvania, in play. That could offset losses Republicans might suffer among Latino voters, forcing the Democratic nominee to overperform significantly among the smaller proportion of nonwhite voters.
The challenge for Mrs. Clinton is, in a sense, reversed from 2008, when she sought to counter Mr. Obama’s appeal to young, liberal and African-American voters. Instead, she sought to rally older, rural, and working-class white Democrats, contrasting her own respect for the Second Amendment with Mr. Obama’s calls for tighter gun control.
This year, she has sought to portray herself as Mr. Obama’s successor, while raising questions about Mr. Sanders’ criticisms of the president. Like Mr. Sanders, she has reckoned with the Black Lives Matter movement, seeking to embrace a younger generation of civil rights activists who have demanded that candidates directly address systemic racism and police brutality.
But it is an open question whether any Democrat can replicate Mr. Obama’s unique relationship with the new voters he galvanized in his two campaigns, particularly black voters. African-Americans turned out widely in 2008 to elect the country’s first black leader and mustered similar strength in 2012 to validate his presidency, angered by what they saw as contempt and disrespect from Republicans.
Mr. Belcher, the Democratic pollster, said that it was far from given that the majority coalition that came out for Mr. Obama would come out again for his successor.
“They came out and they voted for Obama in a record way,” Mr. Belcher said. “The importance then was that these were not Democratic voters — these were Obama voters.”