After almost seeing his campaign grind to a halt, a resurgent Joe Biden seized the momentum in the race to become the Democratic challenger to President Donald Trump with a string of Super Tuesday victories.
This included beating Bernie Sanders in Texas, regarded as a key victory in Tuesday's primaries.
Biden's performance was followed up with fighting talk, when he later tweeted to President Donald Trump that he will dethrone the president come November's elections.
Sanders, a 78-year-old leftist who wants to reshape America's economy, had been the clear leader and was looking for a knock-out blow on the most consequential voting day on the primary calendar.
Instead, the results signalled a remarkable comeback for Biden, a former vice president under Barack Obama who was projected to win at least nine, and possibly 10, of the nomination contests held across 14 states.
Just one week ago the 77-year-old senior statesman Biden saw his campaign teeter on the edge of collapse. Now he is vying once again for frontrunner status.
"It's a good night and it seems to be getting even better. They don't call it Super Tuesday for nothing," Biden told cheering fans in Los Angeles.
Sanders, self-described democratic socialist, was projected to win his home state of Vermont, Colorado and Utah.
He was also ahead in California, the biggest delegate-rich state of all, with a nine-point lead as the count continued on Wednesday morning.
The centrist Biden was projected to win in Virginia, North Carolina, Alabama, Oklahoma, Tennessee, Arkansas, Massachusetts and even Minnesota - a state where Sanders had been expected to win handily.
Well after midnight the projection was made for Biden to win Texas, the second largest US state, and on Wednesday morning he had a narrow lead in Maine with three-quarters of the vote counted. Sanders had been polling ahead in both states.
'We got a tsunami'
"We expected a surge. We got a tsunami," tweeted analyst David Axelrod, chief strategist for Obama's two presidential campaigns. "New race. Completely."
However, a defiant Sanders celebrated his own wins earlier in the night by tearing into Trump, calling him "the most dangerous president in the history of this country."
But he also attacked Biden for having voted for the invasion of Iraq and painted him as tarnished by billionaire contributors.
"We're taking on the political establishment," he said. "You cannot beat Trump with the same-old, same-old kind of politics."
Biden saw the results as proof that his bid to bring American politics back to the center, after four years of Trump's rightwing populism, is on a roll.
"We are very much alive," he told a crowd in Los Angeles. "Make no mistake about it, this campaign will send Donald Trump packing."
A key takeaway from Biden's long list of wins was his strong support among African Americans - a vital piece in any Democratic presidential candidate's coalition.
He seemed to fare less well with the large Hispanic electorate, which in California reportedly went heavily for Sanders. But a victory in Texas, which also has a diverse population, suggests Biden has the capacity to build a broad coalition.
That was bolstered by Biden winning all five other southern states on the ballot Tuesday.
Former New York mayor Michael Bloomberg, 78, and Senator Elizabeth Warren, 70, were the other big-name candidates.
Despite spending record amounts of his own money on advertising, it was an embarrassing debut for billionaire media entrepreneur Bloomberg who failed to win any state -- though he did get a consolation victory in American Samoa, a tiny territory in the Pacific.
Trump weighs in
Trump, who watched the results on television, tweeted his customary insults about the Democrats, deriding Warren for losing her state of Massachusetts.
Biden answered on Twitter, saying: "Come November, we are going to beat you."
Tuesday's 14 contests gave the dwindling Democratic field a giant potential haul of delegates.
Many in the party are desperate to stop Sanders' strong push to win the delegate race, saying the senator will be destroyed in an election where Trump will brand him a socialist bent on ending the American way of life.
Biden was practically counted out after a stumbling early campaign, but first began to rebound with a landslide win Saturday in South Carolina.
That was followed by coordinated decisions by two other moderate candidates -- Pete Buttigieg and Amy Klobuchar -- to withdraw and endorse their former rival.
Bloomberg also now faces calls from within Democratic circles to exit the race and not split the centrist vote.
Biden is making his third White House bid, after failed runs in 1988 and 2008. He argues he can bring a return to "decency" following the tumultuous, scandal-plagued Trump era.
Sanders' fans are convinced only he can take on Trump, who also defied his party's establishment to claim a surprise 2016 victory against Democrat Hillary Clinton.
Supporter Jamison Hanning, a 45-year-old plastics industry technician, said he was "pretty confident" despite Biden's pushback.
"It is just people in the establishment being afraid," Hanning said.