The Democratic campaign for president took another wild and unexpected turn Tuesday night, dramatically lifting the candidacy of former vice president Joe Biden and suddenly putting the onus on Sen. Bernie Sanders (I-Vt.) to demonstrate that he can expand his base of support.

The Democratic contest has been transformed almost overnight from one with many candidates and no clear alternative to Sanders into a head-to-head battle that pits a populist insurgent preaching revolution and democratic socialism against an establishment-backed politician calling for modest change and civility and claiming greater electability against President Trump.

There are few commodities more valuable in political campaigns than momentum, and, right now, Biden is blessed with it in abundance for the first time in his campaign. Biden had a noticeable deficit in money and organization in the Super Tuesday states, compared with the well-resourced and well-organized Sanders.

2020 Democratic presidential candidates reacted as election results came in on Super Tuesday, when 1,357 delegates were up for grabs. (The Washington Post)

The rapid consolidation around Biden’s candidacy has given him what Sanders’s money and ground game could not produce, and the results Tuesday put the former vice president in position to compete on at least an even basis with the senator from Vermont for supremacy in the contest to become the party’s nominee.

For the foreseeable future, the calendar will not get easier for Sanders. In coming weeks, the states holding contests, with some exceptions, were ones that he lost to Hillary Clinton four years ago. In some of the states he won in 2016, the shift from caucuses to primaries could hold down his delegate totals even if he were to win again.

The prospect of Sanders emerging with a sizable lead in delegates after Tuesday’s voting, something that had sparked fears among establishment Democrats that he could be on an unstoppable march to the nomination, began to melt away as the returns came in Tuesday night, with a growing possibility that Biden would be more than competitive by the time all votes were counted.

Results from California, Super Tuesday’s biggest prize with 415 delegates, were coming in slowly early Wednesday morning, with Sanders leading and Bloomberg and Biden trailing. That state, more than any other, was considered the key to Sanders’s hopes of expanding his delegate total.

Texas, where 228 delegates were at stake, was a state Sanders hoped to win, thanks to anticipated support among Latino voters. But after starting the night behind, Biden was declared the winner early Wednesday. The margin, however, remained close enough that the Biden would not be able to gain significantly more delegates than Sanders.

But results from around the country underscored how rapidly fortunes were moving against Sanders. In Vermont, where he won more than 85 percent of the vote in 2016, he was in the low 50s. In Colorado, he won the caucuses in 2016 with nearly 60 percent of the vote. On Tuesday, he was winning with less than 40 percent.

Days ago, many people thought Sanders could win Minnesota over Sen. Amy Klobuchar (D-Minn.). On Tuesday, the state fell into Biden’s column. Biden also won Massachusetts, a state thought to be in competition between Sanders and Sen. Elizabeth Warren (D-Mass.).

Sanders sounded a defiant note when he addressed supporters in Burlington, Vt., and pointed to Texas and California, which together have nearly half of the more than 1,300 delegates at stake, as the linchpins of his Tuesday strategy. He also vowed to wage a fierce fight for the nomination and predicted that he would prevail and go on to defeat Trump in November.

Warren and former New York mayor Mike Bloomberg remain in the race, but neither appeared to have a path to the nomination.

Bloomberg spent roughly half a billion dollars with a plan to make his mark on Super Tuesday. Other than a victory in American Samoa, he was running poorly virtually everywhere and in some places with percentages so low that he would qualify for few delegates. That kind of performance will raise questions about how long he can sustain his candidacy.

Warren hoped to win her home state of Massachusetts and pick up delegates elsewhere, but she, too, was struggling to hit the threshold to qualify for delegates, though she has pledged to continue her campaign through to the convention.

It will take some time to know exactly how the delegates break down from the 14 states voting on Tuesday, but based on what was happening versus what was expected, this was Biden’s night, and the final delegate numbers are certain to reflect the changed circumstances.

Sanders’s victory in Vermont was expected, even though he will not win all 16 delegates as he did four years ago. In addition to Colorado, he also won Utah.

Biden’s victory in Alabama was expected, based on his strength among African Americans, but his victories in Texas, Virginia and North Carolina were hardly a given just days ago. Sanders had competed hard in those states, and pre-weekend polls — which lost their validity after South Carolina — showed a potentially close outcome. Biden also took Tennessee, Arkansas and Oklahoma, the latter a state Sanders won in 2016.

South Carolina provided a shot in the arm for Biden’s candidacy that no one could have predicted, shifting the terrain overnight. The results prompted Klobuchar and former South Bend., Ind., mayor Pete Buttigieg to end their campaigns, and their immediate endorsements of Biden accelerated the consolidation.

There were other elected and former elected officials who joined the Biden team at the same time. Collectively, they sent a signal to the many voters who had decided not to support Sanders but were uncertain where to put their allegiance. Establishment Democrats who a week ago were worrying about how quickly the field might shrink rushed to embrace Biden.

Both the Sanders and Biden campaigns were predicting just before Super Tuesday that the race would go far into the spring and possibly all the way to the July convention in Milwaukee. But the rapidly shifting terrain seen over the 48 hours before Tuesday’s voting changed perceptions and expectations about the balance of strength between the two leading candidates and what it may foreshadow in the coming weeks and months.

The true balance won’t be known until there are complete counts from California, which could take more than a week, or anywhere else where there are questions about how many candidates met the threshold to qualify for delegates. But based on what was known Tuesday night, the race was in a far different place from what anyone expected less than a week ago.

The marquee primary next week will be in Michigan. Sanders scored a major upset there four years ago against Clinton, although his victory margin was narrow. Also on the calendar next week is Missouri, a state Sanders lost by less than a percentage point and where the delegates split almost evenly. Missouri will provide another test of Biden’s and Sanders’s support among African Americans, who make up about a fifth of Democratic turnout in that state.

Because Washington state has switched from a caucus to a primary, Sanders, though favored, will have a more difficult time piling up the kind of delegate margin he did in 2016. Meanwhile, Mississippi should be fertile ground for Biden, as African Americans made up about 70 percent of the Democratic electorate there in 2016 — even more than in South Carolina.

The round of primaries on March 17 includes Arizona, Florida, Illinois and Ohio. Sanders lost Florida badly to Clinton and will face serious resistance again this year because of qualms about his left-wing agenda. He also lost Arizona and Ohio decisively. Only Illinois was close, though Sanders was on the losing end there, as well. A week after that, on March 24, Georgia holds a stand-alone primary, and there again, Biden will be favored based on the size of the African American vote.

No one thought this is where the campaign would be on the night of Super Tuesday.