A week ago, Joe Biden’s campaign was struggling and potentially near collapse. Since then, he has completed one of the most dramatic political turnarounds in recent memory with a string of primary wins that showed him to be the only candidate so far to expand the Democratic electorate, a claim that his top rival, Sen. Bernie Sanders, had made for himself.
The reversal was the result of a combination of signaling from party insiders, beginning with South Carolina Rep. James Clyburn, and more organic decisions by millions of Democrats eager to defeat President Trump in November who quickly coalesced around Mr. Biden, turning him from underdog to potential nomination front-runner.
The electorate that backed Mr. Biden in South Carolina on Saturday and fueled his victories in 10 of 14 states on Super Tuesday had many similarities to the one that boosted his party in the 2018 midterm elections. Suburban voters turned out in droves, along with more traditional elements of the Democratic coalition, particularly African-American voters.
Mr. Sanders’s appeal among the young, the liberal and the politically independent was too weak in many places to create the revolution he promised. Speaking to reporters Wednesday in Vermont, he acknowledged that he hadn’t been as successful as he had hoped in increasing youth voter turnout. “It isn’t easy,” he said.
He also called for a positive campaign between himself and Mr. Biden, before he suggested his opponent is incapable of creating change because he is too closely tied to corporate interests. “What this campaign, I think, is increasingly about, is which side are you on?” Mr. Sanders said.
Rep. Cedric Richmond of Louisiana, a co-chairman of Mr. Biden’s campaign, hit at Mr. Sanders on Wednesday. “As he rails against the establishment, I just did not know that African-American voters in the South were considered part of the establishment,” he told reporters.
In many states, those backing Mr. Sanders were simply outnumbered by more centrist Democrats, who showed far more enthusiasm for voting than four years ago, when former Secretary of State Hillary Clinton was considered the front-runner for her party’s nomination and Donald Trump hadn’t yet come to dominate the nation’s politics. The electorate in many states was older and less liberal than in 2016.
Mr. Biden’s comeback began in South Carolina, where a loss or underwhelming win would have been crippling. Mr. Clyburn’s pivotal endorsement, delivered during a Feb. 26 news conference at a technical college outside Charleston, brought tears to Mr. Biden’s eyes as the congressman spoke of his late wife’s fondness for the former vice president and an elderly constituent who had asked Mr. Clyburn to make his views public.
“I don’t think you can state enough the significance of Jim Clyburn’s endorsement,” said Harold Schaitberger, the general-president of the International Association of Fire Fighters and a longtime Biden friend. “Not only the endorsement but the power of his words.”
Mr. Biden won South Carolina by nearly 30 points. Within 72 hours, about $15 million in fresh donations flowed into his campaign.
Mr. Biden quickly accrued the backing of three former foes: former South Bend, Ind., Mayor Pete Buttigieg, Sen. Amy Klobuchar of Minnesota and former Rep. Beto O’Rourke of Texas. (Former New York Mayor Michael Bloomberg joined the roster of Biden supporters on Wednesday.)
Voters Go to Polls in 14 States on Super Tuesday
Former Vice President Joe Biden storms back into the race for the Democratic nomination, going head-to-head against front-runner Bernie Sanders
Sen. Bernie Sanders at a primary night rally in his home state of Vermont.
Cheryl Senter for The Wall Street Journal
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The late endorsements earned significant media attention and appear to have moved many voters to Mr. Biden just before Super Tuesday, vote totals and exit polls suggest. They also may have helped Mr. Biden earn surprise victories in Minnesota and Texas.
Some 40% of Texas voters who settled on a candidate on election day itself backed Mr. Biden, compared with 10% who voted for Mr. Sanders, exit polls found. The decision process was similar in Minnesota and many other Super Tuesday states.
“This is a case where endorsements were able to drive popular support, rather than the other way around,” said Marty Cohen, a political scientist at James Madison University in Virginia, who has studied the effect of insider endorsements.
The endorsements by Mr. Buttigieg, Ms. Klobuchar and Mr. O’Rourke weren’t coordinated, campaign officials said, but instead were made through individual considerations by the candidates. Mr. Buttigieg made the decision after consulting with aides and former President Obama by phone.
Mr. Biden’s success follows a pattern of voter behavior common in elections, said Joe Trippi, a longtime Democratic strategist. Voters spend the early part of the primary process comparing the party’s candidates to each other. Later, they compare the candidates to the incumbent president they hope to defeat, and their perspective can change.
“After they saw Bernie tie in Iowa, win New Hampshire, win Nevada, then suddenly the voters were confronted with, ‘He is going to be our nominee.’ And then you realize the risks in nominating Bernie against Trump and you ask, ‘What’s the alternative?’ ’’ said Mr. Trippi.
Mr. Sanders has long argued that his brand of government activism would draw a broad coalition of voters eager to defeat Mr. Trump, describing his campaign as “the strongest grass-roots movement of any campaign in modern American history.”
Rep. Emanuel Cleaver, a Methodist preacher, will speak at a rally for Mr. Biden in Kansas City, Mo., on Saturday ahead of that state’s March 10 presidential primary election. Asked to give a preview of his remarks, Mr. Cleaver smiled. “There’s a lot of stuff in the Bible,” he said, “about resurrection.”
Michigan also looms on the March 10 primary slate, and Florida is the biggest prize March 17, as Messrs. Biden and Sanders are headed for a nomination fight that could drag into April or beyond.
William Frey, a senior demographer at the Brookings Institution in Washington who studies political trends, said of the strong turnout of moderate voters: “I think it’s a continuation of the trend we saw in the 2018 midterms, when there was huge turnout. A lot of it is a reaction to Trump.”
White women with college degrees strongly supported Mr. Biden and could be a source of strength for Democrats against Mr. Trump in November. “They did a lot for Biden yesterday,” Mr. Frey said. “That’s going to be a part of the coalition that the Democrats will be banking on.”
Voter turnout jumped by nearly 70% in Virginia over 2016 levels, unofficial results showed, while rising more than 40% in Texas and 16% in North Carolina, all states that Mr. Biden won. Mr. Biden, the man who most embodied the Democratic establishment, won substantial margins among African-Americans, a core Democratic group, as well as older voters.
The twin pillars of Mr. Sanders’s support in 2016—voters under age 30, and political independents—were far less reliable this time around. Those groups either shrank as a share of the 2020 voter pool or were poached by rival candidates.
The senator barely won some of the biggest college communities, including Charlottesville, home to the University of Virginia. Montgomery County, home to Virginia Tech, favored Mr. Biden over Mr. Sanders. In North Carolina, Mr. Sanders won the county that is home to the UNC Asheville, but he lost to Mr. Biden in the home to UNC Chapel Hill.
Worse for Mr. Sanders: For all the talk that he would draw a wave of newcomers to the voter pool, those young voters made up a smaller share of the electorate than in 2016, while the share of voters age 65 and older rose.
Meanwhile, money is continuing to move Mr. Biden’s way. Following his Super Tuesday performance, Mr. Biden attended a Los Angeles fundraiser at the home of former film studio executive Sherry Lansing, and his team has scheduled fundraisers during the month in Bethesda, Md., Chicago, Miami Beach, Phoenix and New York City, including one at the home of Jay Snyder, a principal at HBJ Investments.
Donors including financiers Blair Effron, Mark Gallogly and Marc Lasry have reached out to others recently to rally more financial support for Mr. Biden. “It’s not that hard,” a person familiar with the efforts said. “Who else are you going for?”
—Ken Thomas, Sabrina Siddiqui, Lindsay Wise, Emily Glazer and Eliza Collins contributed this article.
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