Hillary Clinton stops at a polling place in Nashua, N.H., on Tuesday. The next day, her focus immediately shifted to Nevada and South Carolina. (Melina Mara/The Washington Post)

The race for the Democratic presidential nomination turned sharply Wednesday into a battle for Hispanic and African American voters, who are expected to play a decisive role in a long list of upcoming contests in Southern and Western states.

Although former secretary of state Hillary Clinton enjoys a dramatic advantage over Sen. Bernie Sanders (Vt.) among minorities, his resounding victory Tuesday in the New Hampshire primary gives him a shot of momentum that he hopes could turn that tide.

Making clear how crucial minority support will be, Sanders’s first stop after leaving New Hampshire was in Harlem, where he met Wednesday morning with the Rev. Al Sharpton and Benjamin Jealous, the former head of the NAACP.

“If the elections were held today in both those states, we would lose,” Sanders said in an interview, referring to Nevada and South Carolina. “But I think we have momentum, I think we have a shot to win, and if we don’t win, we’ll do a lot better than people think we will.”

Swamped by a wave of populist support for Sanders in New Hampshire, Clinton’s campaign signaled Wednesday that the spectacular loss will not throw her off a careful course set months ago that relies in part on strong support among minorities.

The Rev. Al Sharpton, left, talks with Democratic presidential candidate Sen. Bernie Sanders Wednesday at Sylvia's Restaurant in Harlem. (Richard Drew/AP)

With a blast of announcements about endorsements, travel plans and more, the Clinton campaign sought to turn to subjects — gun control, criminal justice, the water crisis in Flint, Mich. — that speak to African American and blue-collar voters in the states that vote next.

“There is no change to our core argument, our plan, and you saw that in what we are saying as we look to the states that vote in March,” Clinton press secretary Brian Fallon said Wednesday.

The Sanders campaign, meanwhile, predicted that once voters in the next round of nominating states tune in, his message of economic fairness will resonate regardless of race. Sanders has argued that many of his initiatives — including a higher minimum wage, paid family leave and free college tuition — should be more appealing to African Americans and Latinos, given the greater share of economically struggling families in those communities.

Jeff Weaver, Sanders’s campaign manager, said that internal polling is starting to show movement in Sanders’s direction among younger voters of all backgrounds in upcoming states.

“Younger voters are clearly the strongest group for Senator Sanders, and this is sort of reminiscent of the Obama campaign — where younger voters were the president’s strongest bloc as well — across racial lines,” Weaver said.

Clinton had no public appearances Wednesday. She and Sanders meet for another Democratic debate on Thursday in Milwaukee. Clinton is expected to strike a more aspirational, optimistic tone that is a tacit acknowledgment that simply knocking down Sanders’s ideas as unrealistic was not enough.

A chief complaint among Clinton backers appalled by her 22-point loss Tuesday in a state with long and fond ties to the Clinton political franchise is that she isn’t getting through to voters. Exit polling and other data show that Clinton did not connect in New Hampshire — not with men, not with women, not with the young and not with blue-collar voters.

The next two Democratic contests will come in Nevada, where 30 percent of the Democratic electorate in 2008 was black or Hispanic, and in South Carolina, where 55 percent of the 2008 Democratic electorate was black. In March, another slew of Southern states with large African American populations will vote.

Clinton has long been thought to have a Southern “firewall” — an insurmountable advantage with minority voters. Sanders has never demonstrated an ability to attract minorities; his strong showing in Iowa and his trouncing of Clinton in New Hampshire were in states, like his home state of Vermont, where more than 90 percent of the population is white.

An NBC News-Wall Street Journal-Marist poll taken in January in South Carolina showed Clinton with the support of 74 percent of black voters, compared with 17 percent for Sanders.

Tad Devine, a strategist for the Sanders campaign, said that Sanders need not win a majority of black voters in South Carolina in order to put together a coalition with white voters to beat Clinton.

In South Carolina, the Sanders campaign is paying “dozens” of canvassers $15 an hour to go door to door, primarily in the black community, to pitch his candidacy, Weaver said. Cornel West, the noted black scholar who has fallen out of favor with many African Americans because of his sharp criticism of President Obama, also has campaigned extensively in South Carolina for Sanders. Atlanta rapper Killer Mike, another Obama critic, has helped spread Sanders’s message in appearances, online discussions and social-media posts.

Clinton has been quietly organizing in the state since April and has hosted 1,900 grass-roots events. During a recent weekend of campaigning, aides say the campaign contacted 100,000 voters through canvassing and phone banks. Mothers who have lost children to gun violence, including some who were shot by police officers, are planning to campaign on her behalf in South Carolina and other Southern states, and celebrities will be enlisted to visit barbershops and beauty salons to talk up Clinton’s campaign.

“We’re not fighting to win a certain percentage of the vote, we’re fighting to earn the support of the community, we’re fighting for every last vote,” said Marlon Marshall, Clinton’s director of states and political engagement. “She has a multi-decade history of fighting for the African American community. Throughout this entire campaign we’ve seen her go into these communities, have these conversations, talking about issues that matter to the African American community. She’s not just now doing this, she’s done this her whole life, and that’s an important point to make.”

Rep. James E. Clyburn (D-S.C.) predicted that Clinton’s loss in New Hampshire would not shake her support in his state.

“It won’t matter a whole lot,” he said even before the polls had closed in New Hampshire on Tuesday. He said there have been some signs of support for Sanders on college campuses around the state. “There’s not been a big surge. The reliable primary voters that I know don’t seem to have shifted at all.”

Clinton’s African American allies unleashed a wave of criticism against Sanders on Wednesday, strongly criticizing him for being “absent” on issues that matter to black voters — but demonstrating an awareness that she may be vulnerable, in the wake of New Hampshire, to an erosion of support.

“Bernie Sanders as mayor, as a member of the House, as a member of the United States Senate, has been missing in action on issues that are important to the African Americans,” Rep. Hakeem Jeffries (D-N.Y.) said on a conference call with reporters.

In addition to rolling out the support of African American celebrities such as Angela Bassett this week, Clinton landed the endorsement of the South Carolina House Democratic leader, J. Todd Rutherford, who joined in the criticism of Sanders.

Rutherford faulted Sanders for voting in favor of a 1994 Violent Crime Control and Law Enforcement Act, which has been blamed for helping usher in an era of mass incarceration. Bill Clinton, who signed the bill into law as president, has expressed regret for the consequences of the legislation.

Jaime Harrison, chairman of the South Carolina Democratic Party, is remaining neutral because of his post. He pointed squarely to the reasons that African American and female support is crucial to a Democratic victory in his state.

In the most recent competitive Democratic primary, in 2008, 61 percent of the electorate was female, and 55 percent was African American, Harrison said. That combination means that the key voting bloc in South Carolina are black women.

“If you want to know who is going to win, you need to talk to African American women,” Harrison said.

For now, they are predisposed to support Clinton. If Sanders has any chance of making it close or of winning, Harrison said, “he has to cut into her support among African American women.”

Hillary Clinton’s poor showing with young voters and with women of nearly every age in both Iowa and New Hampshire gives many of her allies shivers, and Sanders’s inroads among African Americans have raised alarm.

Sanders has won the support of Jealous, the former NAACP head, and he met Wednesday with him and Sharpton, the civil rights leader. Sharpton said he will wait until a scheduled meeting with Clinton next week before issuing an endorsement.

“My generation was the first generation raised in the era of mass incarceration,” Jealous told reporters after the meeting. “My children are now 3 and 10, and I do not intend for my children to be food for our prisons the way that my brothers and sisters have been. There is no candidate in this race who is fiercer in standing up for those who need allies in the struggle than Bernie Sanders.”

Sanders also scored surprise support Wednesday from influential African American writer Ta-Nehisi Coates, who had earlier excoriated Sanders for not supporting reparations for slavery.

The Congressional Black Caucus is moving quickly to defend Clinton. The CBC’s leaders said they will appear Thursday morning at a club adjacent to the Democratic National Committee to endorse Clinton for president, through the CBC PAC, and then send many of their members to states, including South Carolina, where black voters are crucial.

“It’s one thing to endorse and do nothing. It’s another thing to endorse and to go to work,” said Rep. Gregory W. Meeks (D-N.Y.), chairman of the CBC PAC.

Meeks said that 90 percent of the 20-member board of the political action committee voted to endorse Clinton, none voted for Sanders and a few, including Clyburn, the No. 3 House Democratic leader, abstained because they had not yet endorsed in the race.

Clyburn, in an interview with MSNBC’s “Andrea Mitchell Reports,” reiterated earlier comments to The Washington Post that he is considering endorsing Clinton after previously saying he would stay neutral until the primary vote in his state.

Sanders’s rise, particularly among young voters, even young African American voters, has struck a nerve with veteran members of the caucus who think these voters are behaving naively.

“Many of these are first-time voters, and Senator Sanders’s message resonates with the younger generation because of the promises that he is making,” said Rep. G.K. Butterfield (D-N.C.), chairman of the caucus. “But Mrs. Clinton and others are going to challenge the message by suggesting that it is unrealistic to believe that we can accomplish all of the things that Senator Sanders proposes.”

Scott Clement, Paul Kane and Vanessa Williams contributed to this report.