This time last week, Joe Biden's presidential campaign was all but over.
Barack Obama's vice president had finished fourth, fifth and a very distant second in the first three nominating contests, consistently trailing behind such political behemoths as former South Bend mayor Pete Buttigieg and Minnesota Senator Amy Klobuchar.
One particularly brutal staffer from a rival campaign said there was a "stench of death" around Biden's candidacy.
So how is it possible that Biden just dominated Super Tuesday, winning 10 out of 14 states and reclaiming his long lost frontrunner status?
The answer lies in an astonishing surge of support for him over the course of just 72 hours.
Even at his lowest point, Biden continued to insist that one state, South Carolina, would be his "firewall". Specifically, he was counting on African-American voters to save his campaign.
South Carolina is far more racially diverse than the two first states on the calendar, Iowa and New Hampshire, where Biden did so poorly.
"Up until now, we haven't heard from the most committed constituency in the Democratic Party – the African-American community," a defiant Biden told his dejected supporters after New Hampshire.
"99.9 per cent. That is the percentage of African-Americans who haven't had the chance to vote.
"So when you hear all these pundits and experts on cable TV talk about the race, tell them, it ain't over man, we're just getting started. Our votes count too.
"You can't be the Democratic nominee, you can't win a general election, unless you have overwhelming support from black and brown voters. It's a fact."
At the time, that argument was met with scepticism.
"What matters if you want to win is winning. And the idea that you can sort of skip the first three contests and do well in the fourth – has that ever worked for anybody, ever?" asked Fox News host Tucker Carlson.
"It has not," said Dana Perino, who served as George W. Bush's White House press secretary.
But in the end, Biden was proven right.
The former vice president started to show signs of life with a competent performance in last week's South Carolina debate, even as polls showed Bernie Sanders narrowing his lead in the state to the low single digits.
Then, mere days before the primary, Biden received the crucial endorsement of influential South Carolina Congressman Jim Clyburn.
It mattered. On election day, exit polls showed almost half the voters had been swayed by Clyburn's endorsement.
And Biden won the state – not by single digits, but by a margin of almost 30 per cent.
That victory marked the start of a crazy 72-hour period, during which the moderate wing of the Democratic Party suddenly coalesced, en masse, behind Biden.
He had proven he could win, and that he had the support of African-American voters. That made him the best option to take on Sanders for the nomination, and Donald Trump for the presidency.
The morning after South Carolina, Buttigieg dropped out of the race, admitting he had no path to the nomination.
The day after that, on the eve of Super Tuesday, Klobuchar did the same.
Both former rivals travelled to Texas, where they joined Biden on the campaign trail and officially endorsed him.
"When I ran for president, we made it clear that the whole idea was about rallying the country together to defeat Donald Trump, and to win the era for the values we share," Buttigieg told Democratic voters.
"That was always a goal that was much bigger than me becoming president. And it is in the name of that very same goal that I am delighted to endorse and support Joe Biden for president tonight."
"If you feel tired of the noise and the nonsense in our politics, and if you are tired of the extremes, you have a home with me, and I think you know you have a home with Joe Biden," Klobuchar said.
"Joe Biden has dedicated his life to fighting for people. Not for the rich and the powerful, but for the mum, the farmer, the dreamer, the builder, the veteran. He can bring our country together.
"We do not, in our party, want to just eke by a victory. We want to win big, and Joe Biden can do that."
Biden also won the support of Beto O'Rourke, a popular Texas politician who had dropped out of the presidential race in November.
Billionaire Michael Bloomberg was winning the paid media battle in Super Tuesday states, saturating the airwaves with ads.
But Biden was winning the free media battle, beaming images of a unified, moderate Democratic team into everyone's homes.
The extraordinary consolidation of support around a single alternative to Sanders, in such a short period of time, was the exact opposite of what happened four years ago.
Back then, a number of Republican candidates stayed in the race for far too long, splitting votes between them as Donald Trump notched win after win and quickly became unstoppable.
This time, Buttigieg and Klobuchar did the selfless thing, sacrificing their own ambition for the broader cause. They gave Biden one last, massive boost in the final hours before polls opened.
The scale of Biden's surge quickly became obvious on election night. Exit polls showed a humungous slice of the electorate – nearly half of voters in some states – had chosen their preferred candidate in the last few days.
And among those voters, Biden was winning by miles.
He ended up claiming 10 states. Among them were some astonishing results – Minnesota, won by Sanders four years ago; Texas, with its huge haul of delegates; Virginia, which transformed from being a toss-up to a 30-point Biden triumph in a matter of days.
Biden even blew past his rivals in Massachusetts, consigning home-state Senator Elizabeth Warren to third place.
The former vice president had never even campaigned in some of these states.
"He's winning states that he didn't even attempt to win," CNN anchor Jake Tapper said, barely believing his eyes.
"It's probably the biggest momentum swing I've seen in as short a period of time," said Fox News political editor Brit Hume.
"We've seen, in a 72-hour period, Joe Biden go from being a joke to a juggernaut. That's what happened. And I've not seen anything like this, ever," said political analyst Van Jones.
"To come from this far back with no money, no machine, no organisation, just based on this idea that he can get it done. It's unbelievable."
"I've been helping the party for a very long time. I have never in my life seen anything like what we're seeing tonight," said former Virginia governor Terry McAuliffe.
"You've got to understand, a week ago, Joe Biden was dead.
"In Virginia, not a single television ad was purchased by the Biden campaign. Zero TV ads. Nothing. It's extraordinary, what's happened."
Biden himself was jubilant when he addressed his supporters in Los Angeles.
"Just a few days ago, the press and the pundits had declared the campaign dead. And then came South Carolina. And they had something to say about it," he said.
"We were told, 'When you get to Super Tuesday, it may be over.' Well it may be over for the other guy. Tell that to the folks of Virginia, North Carolina, Alabama, Tennessee, Oklahoma, Arkansas, Minnesota, and Massachusetts.
"I'm here to report we are very much alive. And make no mistake about it, this campaign will send Donald Trump packing. This campaign is taking off."