The fight for the Democratic presidential nomination has reached a critical juncture as millions of American voters from Maine to California head to the polls on Super Tuesday.
Senator Bernie Sanders, who has energised liberals and younger voters, is seeking to pull away from the rest of the field, while former vice president Joe Biden hopes to ride a wave of momentum and establish himself as the standard-bearer for the party’s moderate wing.
The Super Tuesday contests in 14 states are also the first test of billionaire Mike Bloomberg’s massive spending in the Democratic race.
He skipped the first four states, banking on more than half a billion dollars (£390 million) in advertising and ground operations to establish him as a front-runner for the nomination.
The Democratic race has shifted dramatically over the past three days as Mr Biden capitalised on his commanding victory in South Carolina to persuade establishment allies to rally behind his campaign.
Amy Klobuchar and Pete Buttigieg have both endorsed Mr Biden after abruptly ending their campaigns.
Another former competitor, ex-Texas representative Beto O’Rourke, has publicly backed Mr Biden, while a new wave of mayors, politicians and donors said they would support Barack Obama’s former vice president.
Mr Sanders and his closest advisers have pushed back against the shift of party establishment and donor class toward Mr Biden. Campaigning in Minnesota, the senator sought to halt Mr Biden’s momentum with a welcoming message to supporters of Ms Klobuchar and Mr Buttigieg.
He said: “To all of Amy and Pete’s millions of supporters, the door is open. Come on in.
“We all share the understanding that together we are going to beat Donald Trump.”
The dramatic developments came at a key crossroads in the Democrats’ turbulent primary season as the party struggles to unify behind a clear message or messenger in its urgent quest to defeat the president.
Yet as a field that once featured more than two dozen candidates shrinks to just five, the choice for primary voters is becoming clearer.
On one side stands Mr Biden, a 77-year-old lifelong politician who was relishing his newfound momentum in a campaign that has struggled at times to excite voters with a message emphasising a pragmatic approach to governing and modest change.
On the other stands Mr Sanders, a 78-year-old democratic socialist who has scored four consecutive first- or second-place finishes, relying on an energised coalition drawn to his promise to transform the nation’s political and economic systems.
Yet the primary is not just a two-man race.
Mr Bloomberg, in particular, could create problems for Mr Biden’s establishment appeal. The former New York mayor, who will appear on a 2020 ballot for the first time on Tuesday, has invested an unprecedented amount in his presidential bid and racked up many high-profile endorsements of his own.
And Massachusetts senator Elizabeth Warren, who has struggled for delegates and momentum over the last month, has vowed to stay in the race until the party’s national convention in July.
During an outdoor rally on Monday night in East Los Angeles, Ms Warren Mr criticised Biden as she told supporters that nominating a “Washington insider will not meet this moment”, nor will nominating a man “who says we do not need any fundamental change in this country”.
For Mr Biden, the wave of new support could not have come at a better time.
Just two days earlier, a loss in South Carolina would have effectively killed his candidacy. But 48 hours after a massive victory, the former vice president stood on stage in the heart of one of Super Tuesday’s crown jewel states backed by three former rivals and a growing collection of donors, activists and elected officials.
Mr Biden enters Super Tuesday confident in his ability to win states that resemble South Carolina’s demographic makeup: those with large African-American and white moderate populations.
That makes Alabama, North Carolina, Arkansas, Tennessee and Virginia potential Biden victories, even in a splintered field.
Mr Sanders has predicted victory in California, the day’s largest delegate prize. The state, like delegate-rich Texas, plays to his strengths given their significant factions of liberal whites, large urban areas with younger voters and strong Latino populations. Mr Sanders also enjoys obvious advantages in his home state of Vermont, and in neighbouring Massachusetts, where he is eyeing a knockout blow against progressive rival Ms Warren in her home state.
Mr Bloomberg’s stock is at risk of fading as Mr Biden gains ground. But the billionaire will still be a major factor on Tuesday.
The former New York mayor spent much of last week campaigning in a handful of Southern and Western states where his aides say they believe he could notch a win, largely because he is the only candidate who has visited multiple times and pounded the local airwaves with advertisements.
He has focused on Alabama, Arkansas, North Carolina, Virginia, Tennessee and Texas.
Hawaiian representative Tulsi Gabbard also remains in the race.
While Tuesday’s outcome is uncertain, Mr Biden’s team is confident that the trajectory of the race favours them.
“The vice president has momentum,” said Cedric Richmond, a Louisiana congressman and Mr Biden’s national co-chairman.
“You’ll see that in the Super Tuesday states that look more like South Carolina.
Reflecting the growing confidence in the Biden campaign, he added: “We’re going to win Texas.”