Joe Biden powered to a dominating sweep of the South and surprisingly strong showings in New England and the Upper Midwest on Tuesday night, as he sought to seize control of the Democratic presidential race and overtake Sen. Bernie Sanders as the delegate leader.

Sanders was holding on to a lead in California, the state with the biggest delegate haul of the Super Tuesday primaries, as votes were slowly counted there. But Biden’s victories in Texas and eight other states threatened to at minimum erase the lopsided delegate advantage Sanders hoped to gain from the day’s voting. The results set up a more vigorous fight ahead that presents the party with divergent choices, between a pragmatist vowing a return to normalcy and a populist promising a revolution.

Sanders easily won his home state, Vermont, and carried Colorado and Utah.

Former vice president Joe Biden got a boost on Super Tuesday, setting up the Democratic presidential nomination as a fight between him and Sen. Bernie Sanders. (The Washington Post)

But Biden’s victories were significant and widespread, with a string of states across the South offering an early confirmation that his win three days earlier in South Carolina had swiftly and dramatically reshaped the presidential contest.

With most precincts reporting, Biden was winning by double digits in the Super Tuesday states of Virginia, North Carolina, Tennessee, Arkansas and Alabama. He also won Minnesota, Texas, Oklahoma and — in an embarrassment to home-state Sen. Elizabeth Warren — Massachusetts.

In states where he spent little money and no time, and had few field offices, he won as late-deciding voters rushed to support him. Even in a race that has been marked by volatility, the results capped a head-spinning 72 hours.

Sanders just days ago appeared to be en route to a potentially insurmountable lead in delegates after a near-win in Iowa and victories in the second and third contests, New Hampshire and Nevada. Biden seemed on the verge of being forced from the race, after successive fourth-, fifth- and distant second-place showings. But after his mammoth victory in South Carolina, moderates rapidly coalesced behind the former vice president, rivals dropped out and endorsed him, and he racked up margins of victory so large that Tuesday’s races were projected as victories immediately after polls closed.

His win in Virginia testified to the rapid reversal of fortunes. Despite having held only one rally there — and opening only one field office and spending far less than some of his rivals — Biden was on course to win every congressional district and carry the state in a landslide. As soon as polls closed in North Carolina — a state with a strong dose of suburban women and African American voters, both targets for the party and groups that lean toward Biden — he was declared the winner there as well.

His quick wins in Alabama, Arkansas and Tennessee were also largely powered by big margins among women, black voters, moderates and those without college degrees. He also appeared to benefit from high turnout in the same kinds of suburban areas that helped Democrats win the House majority in the 2018 midterms, winning by massive margins in suburbs around Richmond.

Turnout in Virginia was almost double what it was in 2016 and also exceeded 2008 levels.

Late-deciders across the country broke in a major way for Biden. In Virginia, about half of Democratic primary voters said they made their decisions in the past few days, and Biden won about 6 in 10 of them, compared with about 1 in 6 for Sanders, according to preliminary network exit polls. In North Carolina, nearly a third of voters were late deciders, and more than half of them supported Biden, compared with Sanders who garnered about 2 in 10. In Tennessee, where almost 3 in 10 were late deciders, Biden carried more than 6 in 10 of them, compared with less than 2 in 10 for Sanders.

Early results showed a dismal finish for Mike Bloomberg, who has poured some $500 million of his own money into trying to win over voters concerned about Biden’s strength. His only win early in the night was in the caucuses in American Samoa, where he captured 50 percent of the vote.

Rep. Tulsi Gabbard (D-Hawaii) also won a delegate from the U.S. territory in the South Pacific, and under current rules that could allow her to qualify for debates, although the Democratic National Committee indicated it will soon increase the threshold.

It was the most critical day so far for the Democratic nominating contest, with a third of the total pledged delegates up for grabs in 14 states spread around the country and the potential to offer a clarifying moment in a race marked by volatility.

There were 1,357 delegates at stake as the race burst out of the first four states, where the candidates spent the bulk of their time over the past year, and became much more nationalized.

Sanders, with a strong organization and significant financial resources, had been best positioned heading into the night and had been the polling leader in many of the states. But Biden came into Tuesday’s voting amid the best stretch of his campaign and seemed to showcase an ability to leverage the familiarity he’s earned over decades — particularly among older black voters — to overcome other shortcomings.

On Saturday, he walloped Sanders in the South Carolina primary. On Sunday, former South Bend., Ind., mayor Pete Buttigieg, a rival of Biden’s among moderates, dropped out of the race. The next day Buttigieg; fellow moderate Sen. Amy Klobuchar (D-Minn.), who also ended her presidential bid; and another former presidential contestant, onetime congressman Beto O’Rourke of Texas, endorsed the former vice president. A host of other Democrats across the country followed suit.

“It’s still early, but things are looking awful, awful good,” Biden told supporters in Los Angeles on Tuesday night. “For those who have been knocked down, counted out, left behind, this is your campaign.”

Noting that he had been counted out just days ago, he continued, “I’m here to report we are very much alive.”

The Sanders and Biden campaigns were bracing for a protracted fight that could extend to the party’s convention in July, with both now jockeying for position ahead of critical contests over the next two weeks, including several key states in the Midwest.

They disagree on the Iraq War — Biden supported it, Sanders opposed it — and trade deals that Biden has backed and Sanders has railed against. On a host of other issues, Biden holds views that he defines as more moderate and Sanders sees as too incremental.

“Tonight I tell you with absolute confidence, we’re going to win the Democratic nomination,” Sanders told a boisterous crowd in Vermont as results came in, saying he was “cautiously optimistic” about a win in California. “And we are going to defeat the most dangerous president in the history of this country.”

While he was trailing Biden in early results, putting him behind in the hunt for delegates, Sanders’s advisers were confident that they would recoup any early losses with stronger returns in California.

“People who go to sleep tonight at 10 p.m. are going to wake up tomorrow to a totally different race,” said Sanders communications director Mike Casca.

Complicating the one-on-one race between the two men has been the presence of Bloomberg, the billionaire former New York mayor. He skipped the first four contests and appeared on the ballot for the first time Tuesday.

Warren also stayed in the race, like Bloomberg asserting that she would remain a contender until the convention, when she hoped to exert pressure on the party platform, even if she were not the nominee.

Bloomberg spent the day in Florida, a state that does not hold its primary until March 17 but where early voting has started. The former mayor, who less than two weeks ago seemed poised to be the savior for moderates concerned about Biden, refused to set a bar for his own performance in Tuesday’s voting, saying he was not sure he would win any state.

In an address to supporters Tuesday night, he showed no sign of dropping out. “Tonight we proved something very important: We proved we can win the voters who will decide the general election, and isn’t that what this is all about?” he said, emphasizing that while other Democrats spent time in early states, he went to those that flipped in 2016.

After voting at a precinct near her home in Massachusetts, Warren spent Tuesday night in Michigan, a state that will offer the biggest delegate prize next Tuesday.

As she prepared to walk down her front steps, she could hear supporters chanting: “It’s time. It’s time. It’s time for a woman in the White House.” As she walked into a school to vote, children dropped red and white rose petals.

“What I see happening is a lot of folks trying to turn voting into some complicated strategy,” Warren later told several thousand supporters in Detroit. “They are playing games about prediction and strategy. Prediction has been a terrible business.”

But as returns came in, Warren lost her native Oklahoma and was in third place in Massachusetts, the state she has represented for eight years in the Senate.

Early exit polling found that about half of Democratic primary voters in Virginia said Biden is the candidate who would have the best chance of beating Trump in November, while roughly 2 in 10 said Sanders is best positioned to beat Trump. There were similar patterns in three other states voting Tuesday: North Carolina, Oklahoma and Tennessee.

Klobuchar’s departure from the race also seemed to have an impact in Minnesota, where almost 6 in 10 voters said they picked their candidate within the past few days, by far the highest proportion of voters across the nation on Tuesday, according to preliminary exit polls.

Delegates are awarded based on performance statewide as well as in local contests, usually by congressional district. Candidates needed to win at least 15 percent of votes statewide and in any district to gain delegates.

By most traditional measures of strength, Biden trailed badly in many Super Tuesday states. But he did have the less tangible but more forceful benefit of momentum, after his decisive win in South Carolina’s primary drove the most rapid shifts of the contest so far.

After their endorsements, he quickly recorded a video with Buttigieg and featured Klobuchar in a new ad that began airing in Minnesota. Both attempted to create a sense of inevitability and cast him as the only alternative to Sanders. But the ad buy was relatively small and came after many days of early voting.

Michael Scherer in Miami, Sean Sullivan in Burlington, Vt., Cleve R. Wootson Jr. in Los Angeles and Annie Linskey in Cambridge, Mass., contributed to this report.