Where Candidates Won So Far Source: Election results from National Election Pool/Edison Research | Notes: Gray areas were won by candidates who dropped out. Data as of 5 a.m. Wednesday.

Joseph R. Biden Jr. won in states where he didn’t campaign. He won in states where he didn’t have offices. He won in states where he was overwhelmingly outspent in advertising. He won in states where rivals had a better organization.

“They don’t call it Super Tuesday for nothing!” the former vice president roared in an energetic Los Angeles speech that capped the most consequential day yet in the 2020 primary.

The results, from Maine to California, clarified the reality of the race going forward: It is now a two-man contest between Mr. Biden and Senator Bernie Sanders. They were on pace to win the lion’s share of Super Tuesday’s delegates.

See full results from Super Tuesday here.

Mr. Biden won big across the South — Virginia, North Carolina, Tennessee, Alabama, Arkansas — and made surprise incursions in the Northeast, beating Senator Elizabeth Warren on her turf of Massachusetts and even wresting some delegates from Mr. Sanders in his home state of Vermont, where four years ago Mr. Sanders pulled off a clean sweep.

Mr. Biden’s rise coincided with the collapse of Michael R. Bloomberg, the former New York City mayor who spent a half-billion dollars and came away with just one outright victory — in American Samoa. Mr. Bloomberg announced he was suspending his campaign early Wednesday and endorsed Mr. Biden.

But if Mr. Biden was the big story, Mr. Sanders carried the biggest prize and trove of delegates, California, which The Associated Press called just after polls closed. The disparate political coalitions the two septuagenarian politicians have assembled suggest a long and protracted fight ahead.

Here are five takeaways from the biggest day of primary voting and a look at what it means going forward:

Black voters power a resurgent Biden.

Even Mr. Biden seemed taken aback by the breadth of victories that would have seemed nearly unimaginable a few days ago. He won in Minnesota, where barely 36 hours earlier the home-state senator had been strongly favored and where Mr. Biden was not even seriously contesting.

Who Won in Super Tuesday States Races in Maine and California have not been called. Biden Sanders Source: Election results from National Election Pool/Edison Research | Notes: Michael R. Bloomberg won American Samoa. Data as of 5 a.m. Wednesday.

On Mr. Biden’s own website, his “find a field office” page featured only eight offices in the 14 states that voted on Tuesday. (An aide said the total was actually nine.)

But if black voters in South Carolina first fueled Mr. Biden’s recovery over the weekend, they propelled many of his margins on Tuesday. In Alabama, where black voters made up just under half the electorate, he thumped Mr. Sanders among them by more than 60 percentage points, handing him a delegate landslide. He won black voters by more than 50 percentage points in Virginia, and by more than 40 points in Texas — a large enough margin to compensate for Mr. Sanders’s winning margins among white and Hispanic voters, according to the exit polls.

Buoying Mr. Biden’s case against Mr. Sanders is that some of his bigger victories came in states where turnout surged — Texas and Virginia — despite the Vermont senator’s assertion that a tide of younger voters and an expanded electorate would power his “revolution.”

In a race where voters have obsessed about electability, Mr. Biden’s South Carolina victory — and concerns about a surging Mr. Sanders — drove voters and the political establishment to the seeming safe haven of a two-term vice president under Barack Obama.

“Senator Sanders talks about needing a candidate who can generate the enthusiasm and turnout we need to beat Trump this fall,” said Anita Dunn, a top adviser to the former vice president. “Senator Sanders, meet Joe Biden.”

Sanders retains strong support. And the race could soon be a slog.

Super Tuesday was a remarkable comeback for Mr. Biden and comedown from expectations for Mr. Sanders. But that does not mean the race is close to being decided. As of early Wednesday morning, he and Mr. Sanders were both projected to win a similar number of delegates, with the final results from California days or even weeks away.

Who Won the Most Delegates So Far Delegates won in Super Tuesday states are outlined in black. Source: Election results from National Election Pool/Edison Research | Notes: Candidates in gray have dropped out. Data as of 5 a.m. Wednesday.

Mr. Sanders, who has raised far more money than Mr. Biden throughout the contest, continues to have a loyal following among several important constituencies: younger voters, liberal voters and Latino voters, in particular. (The Biden coalition appears strongest among older voters, African-Americans and moderates.)

It is no accident that Mr. Sanders’s support tended to be stronger in the West, which became evident as later results trickled in from states where the electorates are increasingly Hispanic.

One warning sign for Mr. Sanders was that the western states where he was most successful — California, Utah and Colorado — all relied heavily on vote-by-mail balloting that would have blunted Mr. Biden’s late gains.

For Mr. Sanders, the urgent task of halting Mr. Biden’s momentum begins now, and perhaps the biggest test will come next week in Michigan. It is a state that Mr. Sanders carried four years ago against Mrs. Clinton, and a general election battleground that has loomed particularly large for a Democratic Party electorate obsessed with “electability” and beating President Trump.

Plus, the contest could soon see more departures. Ms. Warren has still not finished above third place after 18 states have voted. Progressives are already pressuring her to leave the race to consolidate support for Mr. Sanders.

“Imagine if the progressives consolidated last night like the moderates consolidated, who would have won?” Representative Ilhan Omar of Minnesota, a top Sanders surrogate, wrote on Twitter. “That’s what we should be analyzing.”

Momentum, not political organization or money, is what mattered.

Mr. Biden’s incredible 72 hours between his victory in South Carolina and the first poll closings on Super Tuesday exerted a kind of gravitational pull rarely seen in politics. Three opponents dropped out (Pete Buttigieg, Amy Klobuchar and Tom Steyer) and then three former rivals endorsed him in dramatic fashion on Monday in Dallas (Mr. Buttigieg, Ms. Klobuchar and Beto O’Rourke).

Political operatives marveled at the thoroughness and speed of his consolidation of support. Kevin Cate, a former adviser to Mr. Steyer, noted that the cumulative value of Mr. Biden’s final three days of almost pure positive media coverage amounted to a staggering $72 million, according to Critical Mention, a monitoring company.

The question remained: Would there be enough time for all that to sink in and affect the Super Tuesday results? The resounding answer was yes.

For all of Mr. Bloomberg’s money — he spent more than $100 for every $1 that Mr. Biden invested on television in Super Tuesday states — and the organizational advantages that he and Mr. Sanders had, the momentum and free media attention proved far more important.

In Texas, which Mr. Biden won, he captured half of those who decided on primary day or “the last few days” — well more than double Mr. Sanders, who drew more support among those who decided earlier. It was the same story in Massachusetts. And Maine. And Virginia. Just about everywhere.

How Groups Voted, Based on Timing of Their Decision States are closer to the corner of the candidate that received the most support. Source: Exit polls from National Election Pool/Edison Research | Note: Polls were not conducted in all Super Tuesday states. In some states, sample sizes for some groups were too small to report.

The result left the practitioners of politics agonizing over what it meant for their very profession.

“It’s a bizarre feeling to realize that all the things I obsess over in politics — fund-raising, technology, advertising, field, digital — did not seem to matter very much at all,” was how Shomik Dutta, a veteran of the Obama campaigns and the co-founder of Higher Ground Labs, a group that invests in new progressive technology, put it on Twitter.

Warren and Bloomberg fade.

She was once among the front-runners. He was recently ascendant and spending his way into serious contention.

But on Super Tuesday both Ms. Warren and Mr. Bloomberg badly underperformed. As of early Wednesday morning, Ms. Warren had cracked 20 percent in only a single state, Massachusetts, where she still finished a disappointing third. And Mr. Bloomberg was above 20 percent only in Colorado, where vote-by-mail balloting had insulated him somewhat from the late electoral stampede toward Mr. Biden.

The path forward is uncertain for both candidates.

Ms. Warren, bracing for a rough night, did not plan a prime-time speech and has no public events scheduled yet on Wednesday. (She has more later in the week.) Mr. Bloomberg, in his speech, spoke about his data-centric approach to governance but in a way that could apply to the brutal delegate math he now faces, saying he always would “respect data and tell the truth.”

Bright spots were hard to find for the two candidates. Even places that Mr. Bloomberg’s orbit had been more hopeful about, such as Tennessee and Oklahoma, quickly faded from the campaign’s grasp as the night wore on.

Ms. Warren’s defeat in her home state of Massachusetts was particularly rough, as exit polls showed her finishing in third among women, third in every region of the state and second among liberals.

Her best demographic looked like her: college-educated white women.

The results exposed the party’s generational divide.

One of the biggest fissures in the upcoming battles between Mr. Biden and Mr. Sanders will be generational: Mr. Biden wins older voters by a lot; Mr. Sanders wins younger voters by a lot; they are going to fight fiercely for everyone in between.

How Different Age Groups Voted States are closer to the corner of the candidate that received the most support from the group. Source: Exit polls from National Election Pool/Edison Research | Note: Polls were not conducted in all Super Tuesday states. In some states, sample sizes for some groups were too small to report.

In Alabama — the state where Mr. Sanders performed worst on Tuesday — he still won younger voters (those under 30) by a sizable margin, carrying about 45 percent of them, compared with 32 percent for Mr. Biden, exit polls showed. And in Vermont, Mr. Biden nearly matched Mr. Sanders among those aged 65 or older, while nearly seven in ten voters under 40 went with Mr. Sanders.

The demographic recipe for a Sanders success was winning the next generation in a landslide.

In California, Mr. Sanders carried those under 30 with 72 percent, compared with a paltry 5 percent for Mr. Biden, the exit polls there showed. Mr. Sanders actually won an outright majority of Californians under 44 and battled Mr. Biden to a draw among voters 45 to 64 years old. It was a similar coalition that led to his sweeping victory in Nevada in late February.

For Mr. Biden, winning typically involved strongly consolidating the oldest voters (he won three-quarters of those above 65 in Virginia, for instance) while limiting Mr. Sanders’s gains among those under 30.

Going forward, the primary seems likeliest to be eventually determined by whoever can capture those between 40 and 65.