WASHINGTON – Sen. Bernie Sanders, whose call for a liberal agenda galvanized millions of followers, dropped out of the presidential race, giving former Vice President Joe Biden a clean path to the 2020 Democratic nomination.

Sanders' exit comes after a string of losses to Biden in the primary election.

The intensifying coronavirus pandemic meant he could no longer hold the large rallies that came to define his grassroots movement, though he often pointed to the problems many Americans had getting tested and treated for the virus as evidence that the country needed to adopt his signature "Medicare for All" proposal.

In a speech Wednesday, Sanders congratulated Biden on being the Democratic nominee. He called Biden a "decent man" whom he plans to work with to "move our progressive ideas forward."

"Then, together, standing united, we will go forward to defeat Donald Trump," he said.

He thanked his supporters, who propelled him in two presidential campaigns.

"I want to express to each of you my deep gratitude for helping to create an unprecedented grassroots political campaign that has had a profound impact in changing our nation," Sanders said. "Together, we have transformed the American consciousness as to what kind of nation we can become and taking this country a major step forward in the never-ending struggle for economic justice, social justice, racial justice and economic justice."

Fiercely unapologetic, Sanders' call for economic justice, nationwide health care and an end to the "billionaire class" was the loud refrain for two presidential campaigns that tried to pull the Democratic Party to the left.

Referring to his campaign's policies, Sanders said Wednesday, "It was not long ago that people considered these ideas radical and fringe. Today, they are mainstream ideas, and many of them have already been implemented in cities across the country. That is what we have accomplished."

But ultimately, it fell short. For the second consecutive election, the self-described Democratic socialist was the runner-up, finishing behind Hillary Clinton in 2016 and the former vice president this year.

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"I wish I could give you better news, but I think you know the truth," Sanders said Wednesday. "And that is that we are some 300 delegates behind Vice President Biden, and the path toward victory is virtually impossible. … It's been a very difficult and painful decision."

Moments after Sanders' announcement, Biden thanked the Vermont senator in a lengthy statement, noting Sanders' "impact on this election and on elections to come is far from over."

"Bernie has put his heart and soul into not only running for President, but for the causes and issues he has been dedicated to his whole life," Biden said in the statement. "So I know how hard a decision this was for him to make – and how hard it is for the millions of his supporters – especially younger voters – who have been inspired and energized and brought into politics by the progressive agenda he has championed."

Biden said he and his wife, Jill, thanked Sanders and his wife, Jane, for the difficult decision to suspend the campaign.

"You have put the interest of the nation – and the need to defeat Donald Trump – above all else. And for that, Jill and I are grateful," Biden said. "But we also want you to know: I’ll be reaching out to you. You will be heard by me. As you say: Not me, Us."

Sanders says he will remain on ballots to earn delegates

Sanders said Wednesday he's going to stay on the ballot in the remaining primary states to earn delegates.

"While Vice President Biden will be the nominee, we must continue working to assemble as many delegates as possible at the Democratic convention, where we will be able to exert significant influence over the party platform and other functions," Sanders said. "Then together, standing united, we will go forward to defeat Donald Trump, the most dangerous president in modern American history."

Sanders entered the 2020 campaign with high name recognition, experience and an army of supporters – some pejoratively known as "Bernie Bros" – that collectively propelled him into front-runner status after the first three states.

His momentum fizzled after the South Carolina primary Feb. 29 when black voters backed Biden in large numbers, foreshadowing the struggles Sanders would have with a key Democratic constituency going forward into Super Tuesday three days later.

Sanders won the biggest Super Tuesday prize – California – but he lost 10 of the other states to Biden that night, including Texas, a state in which he had invested a lot of time and energy. After that, he never regained his footing while support from rivals such as Michael Bloomberg and Amy Klobuchar coalesced around Biden.

He also had a health scare.

In early October, he felt chest discomfort during a campaign event in Las Vegas. His campaign announced that he had a blockage in one artery, and two stents were inserted. Several days later, Sanders' treating physicians Arturo Marchand and Arun Gururaj released a statement via the campaign saying Sanders had a heart attack.

Brian Monahan, the attending physician at the U.S. Capitol, declared the senator in "good health" in a letter released Dec. 30, 2019, by the Sanders campaign. Monahan is Sanders' primary doctor.

A New York City native who never shed his thick Brooklyn accent, Sanders, 78, built a national following despite representing the nation's second least populous state. His supporters were overwhelmingly under 35, providing the energy to his dynamic campaign but not always showing up at the polls when he needed them most.

His political career nearly never happened. In 1981 at age 39, the carpenter and documentary filmmaker was elected mayor of Burlington, Vermont's largest city, by only 10 votes out of nearly 10,000 cast.

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He was elected nearly a decade later as Vermont's sole member of the U.S House. After eight terms, he won a seat to the U.S. Senate in 2006, using his perch on Capitol Hill to craft a platform on national issues that became the basis of his presidential runs.

Sanders, whose state has no party registration, is the longest-serving independent in U.S. congressional history.

Sanders was a relative unknown and a long-shot candidate (he was 50 points behind Clinton in some national polls) when he launched his first presidential campaign in the spring of 2015.

Before his first presidential run in 2016, Sanders' outrage over the “billionaire class” might have been captured only on C-SPAN and left-leaning news shows. His presidential run changed that.

Sanders won 22 states and 45% of the pledged delegates, and he consistently led Clinton overwhelmingly among 18- to 29-year-olds. His campaign drew a record 8.2 million individual contributions from about 2.5 million donors, raising about $228 million largely through fundraising emails to supporters.

2020 Democratic Primary Election Results | USA TODAY

His call for a "political revolution" quickly gained momentum on social media, igniting a "feel the Bern" fever that drew nearly 1.5 million people to his rallies and other events across the country in a wave of populism similar to the one that helped propel Republican Donald Trump to the White House.

Though he lost, Sanders' influence was evident. Clinton proposed expanding access to health care and eliminating college tuition for working families. Many of his priorities were included in what Sanders described as the most progressive platform in the party's history.

Former opponents praise Sanders' campaign and values

Sanders’ onetime Democratic presidential rivals praised his campaign and struck a united tone as they look to help Biden defeat Trump.

U.S. Sen. Elizabeth Warren, D-Mass., who as presidential candidate competed against Sanders for support from the left, thanked Sanders for “fighting so relentlessly for America’s working families during this campaign.”

“Your fight for progressive ideas moved the conversation and charted a path for candidates and activists that will change the course of our country and party,” Warren tweeted.

U.S. Sen. Kamala Harris, D-Calif., called Sanders “an extraordinary leader” whose campaign “drove the conversation” around issues for working families. “We must continue that spirit and ethos as we work to unite the party to defeat Trump,” she said.

Sen. Klobuchar, D-Minn., said Sanders’ decision to end his campaign “is a decision to unite our party and shows he is a true public servant.”

Former South Bend, Indiana, Mayor Pete Buttigieg said he loved getting to know Sanders on the campaign trail.

2020 Democratic Primary Election Results | USA TODAY

“He and his supporters are a tremendous force, and I’m looking forward to teaming up to end the Trump presidency and open the door to a better American era,” Buttigieg tweeted.

Sanders said Wednesday his presidential bid was never "just a campaign."

"We are a grassroots multiracial, multi-generational movement, which has always believed that real change never comes from the top on down but always from the bottom," he said.