For much of 2019, former Vice President Joseph R. Biden Jr. was a steady and certain presence near the front of the Democratic presidential race. No amount of speed bumps — verbal gaffes, criticism of his long record as a Washington politician, even attacks from Republicans over his son’s dealings in Ukraine — could dislodge him from that position, much less sink his candidacy.
But then the caucusing and voting began.
Over the next six weeks, Mr. Biden’s campaign would journey to the edge of collapse after two disastrously poor finishes in the Iowa and New Hampshire nominating contests, before rebounding slightly in Nevada and then upending the dynamics of the race entirely with a dominating victory in South Carolina. Riding that newfound momentum, Mr. Biden pressed forward with a strong performance on Super Tuesday followed by several more triumphs, winning crucial states like Michigan and commanding the South across the board.
And then the coronavirus hit, transforming the nature of campaigning and voting for the rest of the year and leaving the race at a standstill, with Mr. Biden in the lead.
On Wednesday, Senator Bernie Sanders of Vermont dropped out of the race, leaving the former vice president as the presumptive Democratic nominee.
Here’s a timeline charting Mr. Biden’s early slide, his remarkable rise and his awkward plateau.
Polls ahead of the Iowa caucuses show strength for Sanders
In the days leading up to the Iowa caucuses, national polls and surveys of early-voting states showed Mr. Biden’s position weakening and Mr. Sanders coming on strong, especially in the first two nominating contests, Iowa and New Hampshire. A Des Moines Register poll in early January, for instance, found that Mr. Sanders had a five-percentage-point lead in Iowa, and a poll conducted for CNN a week before the caucuses showed him leading Mr. Biden nationwide, 27 percent to 24 percent.
A fourth-place finish in Iowa
Mr. Biden never expected to win Iowa — a state where he had a track record of performing poorly in his previous presidential bids. And while he received coveted endorsements this time around from well-known Iowans like former Gov. Tom Vilsack and his wife, Christie Vilsack, they did not end up doing him much good.
But even with lowered expectations, Mr. Biden’s fourth-place finish in Iowa was a considerable blow, and it set a grim tone for the campaign as it slogged ahead. The loss exposed cracks in Mr. Biden’s campaign infrastructure that presaged a number of changes. Even his status as the race’s leading moderate came into question as former Mayor Pete Buttigieg of South Bend, Ind., won a narrow victory in Iowa over Mr. Sanders.
“I am not going to sugarcoat it,” Mr. Biden said days later as he campaigned in New Hampshire. “We took a gut punch in Iowa.”
Disaster for Biden in New Hampshire
In what may have been the lowest point for Mr. Biden’s campaign, the former vice president followed up his disheartening performance in Iowa with a fifth-place finish in New Hampshire, below the viability threshold, and without earning any delegates from the state. And his moderate rivals, Mr. Buttigieg and Senator Amy Klobuchar of Minnesota, finished second and third behind Mr. Sanders and continued to gain traction.
Perhaps in anticipation of an embarrassing defeat, Mr. Biden left New Hampshire the day of the primary and flew to South Carolina to continue courting that state’s predominantly black Democratic voters.
“We’re going on and we’re going to win in Nevada and in South Carolina,” he promised supporters in a live stream.
Sanders runs away with Nevada
Mr. Sanders went on to claim a resounding victory in the Nevada caucuses. His triumph by more than 25 percentage points widened his delegate lead. It also established him — at least for the moment — as the race’s clear front-runner and provided evidence that he had, in fact, built the multiracial coalition he had promised.
Inside a Las Vegas union hall, Mr. Biden sought to frame his second-place finish as something of a comeback while also vowing victory in the next contest, South Carolina.
“Y’all did it for me,” he told supporters before taking aim at Mr. Sanders and Michael R. Bloomberg, the billionaire former mayor of New York who was at the time a challenger for the party’s moderate voters. “I ain’t a socialist, I ain’t a plutocrat, I’m a Democrat.”
Biden makes his case at the South Carolina debate
As the race’s front-runner, Mr. Sanders took fire from all sides in what was a chaotic, messy debate before the South Carolina primary. Some of the attacks came courtesy of Mr. Biden, who hit Mr. Sanders on his comments about Cuba and on his opposition to certain forms of gun control.
But Mr. Biden also made clear just how important winning South Carolina was to the continued viability of his campaign. He vowed to win the primary; attacked Tom Steyer, the billionaire investor who had spent heavily in the state; pledged to appoint a black woman to the Supreme Court; and invoked his relationship with former President Barack Obama.
In past debates, Mr. Biden’s performances had been uneven. But experts and analysts generally said they thought that on a night he desperately needed a strong showing, Mr. Biden did enough.
James Clyburn endorses Biden
The next morning, Representative James E. Clyburn, the highest-ranking African-American in Congress and one of South Carolina’s most powerful political figures, endorsed Mr. Biden.
“I’m voting for Joe Biden and South Carolinians should be voting for Joe Biden,” Mr. Clyburn said as the former vice president looked on. “I know Joe. We know Joe. But most importantly, Joe knows us.”
Mr. Clyburn’s announcement was not a surprise, but it appeared to have a seismic effect on how South Carolinians voted days later.
Dominance in South Carolina
Despite all of Mr. Biden’s earlier struggles, his so-called firewall in South Carolina more than held up, delivering him a decisive victory there that would change the trajectory of the race. Mr. Biden drew on the strength of his decades-long relationships in the state and on his close bond with black voters to crush the rest of the field, winning more than 48 percent of the vote and every county in South Carolina.
The success put Mr. Biden in a exuberant mood for his victory speech, in which he looked ahead to Super Tuesday and made repeated arguments, at least implicitly, against Mr. Sanders.
“If Democrats want a nominee who’s a Democrat, a lifelong Democrat, a proud Democrat, an Obama-Biden Democrat, join us,” Mr. Biden said. “We have the option of winning big or losing big. That’s the choice.”
The Democratic establishment falls in line
The results in South Carolina also had reverberations beyond Mr. Biden and Mr. Sanders, who finished in a distant second place. Mr. Buttigieg and Ms. Klobuchar both finished in the single digits — poor showings that proved fatal to their campaigns.
Just a day after Mr. Biden’s victory in South Carolina, Mr. Buttigieg exited the race; Ms. Klobuchar did the same the next day and immediately endorsed Mr. Biden. Hours later, the two former presidential candidates joined former Representative Beto O’Rourke of Texas and all three put their weight behind Mr. Biden in Dallas on the eve of Super Tuesday.
A cascade of Biden endorsements from Democratic mayors, senators and governors quickly followed, with many emphasizing the need for party unity to defeat President Trump in the general election. Collectively, they made clear that mainstream Democratic leaders had coalesced behind a single candidate.
A Super Tuesday triumph
“They don’t call it Super Tuesday for nothing!” an enthusiastic Mr. Biden told supporters in Los Angeles on his way to winning 10 states and hundreds of delegates, showing he had fully revitalized his campaign.
When the dust finally settled on the Democratic primary race’s biggest day, the state of the nominating contest had fundamentally changed. Mr. Biden had won North Carolina, Texas and Virginia with the backing of African-Americans and moderates; Mr. Sanders had leaned on the support of liberals and young voters to claim California; and the race now had two front-runners.
At the same time, it was clear that the momentum had shifted in Mr. Biden’s favor. The Super Tuesday contests showed that Mr. Biden was both garnering support from black voters and turning out voters in the suburbs; Mr. Sanders suddenly faced questions about why youth voter turnout appeared to be flagging.
“This is your campaign,” an energized Mr. Biden said during his Super Tuesday victory speech. “Just a few days ago the press declared the campaign dead. And then came South Carolina. And they had something to say about it. And we were told when we got to Super Tuesday it would be over. Well, it may be over for the other guy.”
Bloomberg stands down and backs Biden, and others follow suit
Mr. Sanders was not the only candidate damaged by Mr. Biden’s rise. Mr. Bloomberg, who had joined the race in part to provide a moderate alternative if Mr. Biden faltered, dropped out of the race and endorsed the former vice president the day after Super Tuesday.
Mr. Bloomberg’s network of advocacy groups and many elected officials who had backed the former mayor quickly followed suit. And in the coming days, Senators Cory Booker of New Jersey and Kamala Harris of California — both former presidential candidates — would also offer their support to Mr. Biden.
Biden solidifies his success with another series of victories
The “Joementum” spilled into another important Tuesday, as Mr. Biden took command of the race, notching victories in Missouri, Mississippi and Michigan — the biggest prize of the night — in quick succession. He would follow up those successes by winning Idaho and Washington State, leaving only North Dakota for Mr. Sanders on a night that six states voted.
Mr. Biden’s successes in Michigan and Washington State were particularly crushing to Mr. Sanders, who had won a stunning upset in Michigan during his 2016 presidential bid and had hoped to do well in the West Coast state of Washington, which had appeared demographically advantageous to him.
The March 10 results solidified Mr. Biden’s coalition of black voters, female voters, older voters and white voters with college degrees, providing a clearer sense of what a Biden coalition could look like moving forward.
At the same time, Mr. Sanders’s path to the nomination became incredibly narrow.
“I want to thank Bernie Sanders and the supporters for their tireless energy and their passion,” Mr. Biden said in Philadelphia. “We share a common goal. Together we’ll defeat Donald Trump.”
Campaigning during a pandemic
Soon afterward, the world changed. The novel coronavirus, which had already started to affect may parts of everyday life, completely upended the campaign.
Standing six feet apart, Mr. Biden and Mr. Sanders faced off at a debate with no studio audience on March 15. Two days later, Mr. Biden easily swept Arizona, Florida and Illinois, leaving almost no path for Mr. Sanders and solidifying the former vice president’s strength in the Midwest and the Southeast.
Ohio was also supposed to have a primary on March 17, but the governor ordered precincts closed because of the coronavirus. A wave of other states pushed back their primaries to late April or June in hopes the pandemic would subside by then.
The halting effect of the virus solidified Mr. Biden’s lead in the race — he now has 1,217 delegates to Mr. Sanders’s 941 — but also pushed him largely off the campaign trail.
He is struggling to find his role during the public health crisis as the presumptive Democratic nominee, and is trying to find new ways to connect with voters and break through in the news media. He has spoken increasingly openly about his process of choosing a running mate, who he has promised will be a woman. He started a podcast. He has hosted virtual happy hours even though he doesn’t drink.
In many ways, Mr. Biden is back to where he was when he entered the race: acting as the Democratic standard-bearer, facing a daunting general election against Mr. Trump.