In January 2019, it was reported that it is certain Sanders would enter the 2020 primary race following his lead in the contested race and an announcement would be immediate. On February 15, 2019, it was reported that Sanders recorded his presidential announcement video for a 2020 bid. He announced his second presidential bid on February 19, 2019.
On March 2, 2019, Sanders held his first presidential rally in Brooklyn College in New York City. The next day, Sanders held a second rally at Navy Pier in Chicago. About 13,000 people went to the Brooklyn rally and 12,500 went to the Chicago rally.
On March 5, 2019, Sanders signed a formal statement, called a "loyalty pledge", saying that he is a member of the Democratic Party and will serve as a Democrat if elected. The day before, he had signed paperwork to run as an independent for re-election to his Senate seat in 2024. Later that month, national polling had Sanders and former Vice President Joe Biden tied for the Democratic primaries.
In January 2020, national polling showed Sanders in second place with 16% behind Biden's 28%, a three point gain for Sanders since last polling.
On April 6, 2019, Sanders was part of a Fox News town hall that had more than 2.55 million viewers. Sanders's appearance on Fox News saw an increase of Fox News viewers by 24% overall and 40% in the 25-to-54-year-old demographic.
During the first four Democratic primary debates, Sanders appeared near the center stage, as one of the highest polling candidates. During the July and September debates, Sanders and Elizabeth Warren were described by commentators as having a "non-aggression pact", talking about progressive positions which were different than positions from the other candidates.
Within three-and-a-half hours after his announcement, Sanders had raised over $1 million from small donations from all 50 states, breaking the record held by Senator Kamala Harris after her presidential announcement. Within 12 hours, Sanders had raised over $4 million from 150,000 donors, and in the first 24 hours following his announcement, Sanders raised $5.9 million from 225,000 small donations, with the average donation being $27. In November 2019, Sanders said his campaign had over four million donations from individual donors, the largest than any other presidential candidate in American history.
In January 2020, Sanders raised over $34.5 million during the fourth quarter of 2019, the largest of any 2020 Democratic presidential campaign.
In April 2019, a national poll had Sanders leading Biden 29% to 24% among Democratic voters for the primaries.
Sanders polled between 15-20% on most national surveys between May and September of 2019. In September 2019, Warren and Sanders remained in a virtual tie for second place. Some surveys showed Warren ahead of Sanders, while others showed Sanders ahead of Warren.
National surveys of a potential general election matchup with Donald Trump showed Sanders leading by an average of 6.5% as of September of 2019, compared to a 11.7% lead for Biden and a 5% lead for Warren. The average of polls in New Hampshire in August and September of 2019 showed a virtual tie between Sanders, Warren, and Biden. After constantly being behind Warren and Biden in the polls, in November 2019 Sanders saw a rise in polls beating Warren for the second place spot behind Biden.
In January 2020, an Iowa poll found Sanders tied for first place behind Biden and Pete Buttigieg with 23%. The same poll found Sanders in first place in New Hampshire with 27% and Biden in second with 25%. A few weeks later, Sanders was leading in a nationwide poll with 27% against Biden's 24%.
On February 10, 2020 following the Iowa caucuses, a national poll had Sanders leading the race with 25% while Biden fell to 17%. A few weeks later on February 27, a new Fox News national poll showed Sanders at 31% with Biden at 18%. After Super Tuesday in March, Biden began to expand his lead over Sanders.
On February 3, 2020, the Iowa caucuses were held, however, due to an issue with apps used to count the votes and spread the delegate votes, the results were announced the following day. The next day, 71% of the votes were released showing Pete Buttigieg leading Sanders by less than 2%. On February 10, Sanders and Buttigieg asked for a recount. The overall results, Sanders won the popular vote winning 45,842 (26.5%) while Buttigieg won 26.2% of the state delegates equivalents to Sanders' 26.1%. On February 27, Buttigieg was declared the winner of the Iowa caucus despite Sanders winning the popular vote.
On February 11, 2020, Sanders won the New Hampshire primary winning almost 26% of the vote compared to Buttigieg's 24%. On February 23, Sanders won the Nevada caucus in a landslide victory winning 40% of the popular vote and 47% of the county convention delegates. Following the race, Sanders became the Democratic front-runner leading with 34 delegates and nearly 26% of the popular vote. He also became the first presidential candidate, Democrat or Republican, to win the popular vote in the first three primary states in a row. In February 29, Sanders lost the South Carolina primary winning nearly 20% of the vote to Biden's 48%.
During Super Tuesday on March 3, 2020, Sanders won the California, Utah, Colorado and Vermont contests. He lost American Samoa to Michael Bloomberg and Alabama, Arkansas, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, Texas, and Virginia to Joe Biden. On March 11, Sanders won the North Dakota caucus, but lost the Michigan, Mississippi, Missouri, Washington, and Idaho primaries to Biden. On March 14, Sanders won the Northern Mariana Islands caucus. On March 18, Sanders lost the Arizona, Illinois and Florida primaries. On March 23, Sanders won the Democrats Abroad primary winning 58% of the vote compared to Biden's 23%.
Sanders lost the Alaska primary on April 11, 2020 after winning 44.7% of the vote to Biden's 55.3%. Two days later, Sanders lost the Wisconsin primary to Biden with a 63.8% to 30.9% margin.
On April 8, 2020 one day after the Wisconsin primary, Sanders ended his campaign after failing to beat Biden in many primary contests after Super Tuesday. He said that he would stay on the ballot in the remaining states and continue to keep delegates with the goal of influencing progressive ideas to the Democratic Party and Biden's campaign. On April 13, Sanders endorsed Biden for President.
In a May 2020 interview, Sanders said that there is a "very, very slim chance" that he would run for a third time in 2024.
Sanders spoke on the first day of the 2020 Democratic National Convention on August 17, 2020.
Following Biden's victory in the election, he was seen as a possible cabinet pick for United States Secretary of Labor in the Biden administration. Sanders said that he would accept the position if Biden offers him the nomination. He asked for the support from Senate allies to labor unions for his chances to become Biden's Labor secretary. In January 2021, Biden picked Mayor of Boston Marty Walsh to be his Labor Secretary. Biden said he thought about picking Sanders but did not want to risk the soon-to-be U.S. Senate Democratic majority.
Sanders married Deborah Shiling in 1964. The couple divorced two years later in 1966. He met his second wife, Jane O'Meara, when Sanders became mayor of Burlington, Vermont in 1981. They were married in 1988. Sanders has a son, Levi Sanders, who was born out of wedlock with his domestic partner Susan Campbell Mott. Sanders and Mott were partners only one year before splitting in 1969. Sanders has three step-children from O'Meara: Dave, Carina and Heather Driscoll. He thinks of them as his own children. His brother, Larry, was a Green Party County Councillor representing East Oxford in England until his retirement in 2013.