The 2020 Democratic primary season featured one of the largest fields ever, with 28 serious contenders competing to take on President Donald Trump in the November general election. The group included a record number of women — six — as well as the first openly gay major candidate and two billionaires.
It was a battle of gender, race and age with a range of ideas that pitted progressive agendas and democratic socialism against the moderate establishment.
Candidates who qualified participated in 11 debates that provided some heated exchanges on topics such health care, gun control, climate change, immigration reform, race relations, universal basic income, and a wealth tax. Candidates also had to navigate their campaigns amidst an historic impeachment battle that sidelined four senators still in the race during the trial.
The coronavirus pandemic across the U.S. forced the last two candidates standing, Sen. Bernie Sanders, 78, and former Vice President Joe Biden, 79, to cancel rallies and move their campaigns online for the safety and health of their supporters, and to comply with stay-at-home and social distancing orders.
After more than a year of campaigning, Sanders announced he was ending his bid for the nomination on Wednesday, effectively leaving Biden as the apparent nominee.
The following are some of the key moments that highlighted the unprecedented primary season.
Dozens of candidates entered — but only one could win. Sens. Amy Klobuchar, Cory Booker, Kamala Harris and Kirsten Gillibrand, as well as former Texas Rep. Beto O'Rourke all launched campaigns with high expectations from pundits and supporters.
Among candidates thought to face longer odds: Pete Buttigieg, the first openly gay major Democratic presidential candidate, launched his campaign with a historic kiss with husband Chasten. Buttigieg, then mayor of South Bend, Indiana, went on to become a top contender.
Buttigieg faced scrutiny over his record on race back home. The criticism grew after CNBC first reported on Buttigieg's record in April 2019.
Sanders, who essentially never stopped campaigning for president after his failed 2016 bid, surprised pundits with the success of his 2020 operation. Sanders outdid the rest of the field in raising money via small dollar donations. His "Medicare for All" health-care proposal became one of the top issues during the primary.
The first debates had a total of 20 candidates that qualified. The record-breaking number of debate participants was broken into groups of 10 over two nights.
The first major shakeup of the race came after Harris attacked on Biden over busing and his past work with segregationist senators. The move propelled her into second place in national polling averages, though the California lawmaker failed to maintain her momentum.
Biden faced his next major threat from Sen. Elizabeth Warren. Warren rose to first place in national polling averages for a brief period in early October on the strength of her populist appeal and well-organized campaign operation. The Massachusetts progressive, who made waves going after billionaires and promoting her numerous plans, lost steam after she released a complicated plan to pay for "Medicare for All." She did not gain it back.
Health troubles looked likely to doom Sanders's bid. After suffering a heart attack that knocked him off the trail, Sanders re-emerged at a rally in New York with Rep. Alexandria Ocasio Cortez that reinvigorated his bid. "I am back," he told supporters.
The first voting of the primary came more than a year after campaigning began in earnest — and did not go as planned. Tech troubles doomed Iowa's first-in-the-nation caucuses. Buttigieg and Sanders both vied for the lead in the state, but NBC News did not call a winner amid irregularities in the data. The fiasco of the Iowas Caucus resulted in the resignation of Troy Price, chairman of the Iowa Democratic Party.
Andrew Yang brought something different to the 2020 race. While the businessman never sustained a polling average above 5%, his pitch for a universal basic income brought the proposal into the national dialog. Yang attracted a large, engaged online following, and became known for his quirky merchandise, including "MATH" hats.
Democratic senators were forced off the campaign trail by a historic impeachment trial in the Senate. Trump, impeached on charges that he coerced the government of Ukraine to open up investigations into Biden's family, denied the allegations and was ultimately acquitted.
The former mayor of New York spent nearly a billion dollars on his presidential campaign — but, in the end, failed to gain traction. He left the race shortly after Super Tuesday.
A rift developed between fellow progressives Warren and Sanders after Warren claimed that Sanders told her during a private meeting that he did not believe a woman could beat Trump in 2020. The topic came up during the Democratic debate in January, after which Warren refused to shake Sanders's hand. Billionaire candidate Tom Steyer found himself in the middle of things.
Hawaii Rep. Tulsi Gabbard was the last candidate standing besides Sanders and Biden when she left the race in March, endorsing the former vice president. She garnered just two delegates out of the nearly 2,000 needed to win.
The most influential politician in South Carolina, Majority Whip James Clyburn, lent his support to Biden just ahead of the state's primary. The endorsement helped Biden carry the state — his first win in three presidential runs — which proved to be pivotal for his remarkable turnaround.
Following his victory in South Carolina, Biden racked up endorsements from vanquished rivals O'Rourke, Klobuchar and Buttigieg, sending him to victory on Super Tuesday, and fueling his momentum.
Biden and Sanders started to move their campaigns online in March over coronavirus concerns, as the toll of the pandemic in the U.S. became undeniable. COVID-19 would reshape campaigns, fundraising, debates and elections.
On Wednesday, Sanders officially suspended his campaign. "I cannot in good conscience continue to mount a campaign that cannot win and which would interfere with the important work required of all of us in this difficult hour," Sanders said in live-streamed remarks from Vermont. "Let us go forward together, the struggle continues," he said.
With Sanders out, the head-to-head battle between Biden and Trump — long expected — began at last.