Bernie Sanders has suspended his presidential campaign.

The US senator from Vermont, the longest-serving independent in the history of the Congress, was once again seeking the Democratic nomination. But he announced Wednesday, April 8, that he was dropping out.

Four years ago, Sanders was viewed as a protest candidate from the political fringe. But after finishing second to Hillary Clinton, he became one of the most popular politicians among Democratic voters.

Now it appears that he will fall short once again, this time to former Vice President Joe Biden.

Sanders, right, leads a sit-in organized by the Congress of Racial Equality in 1962. The demonstration was staged to oppose housing segregation at the University of Chicago. It was Chicago's first civil rights sit-in.
Sanders, right, leads a sit-in organized by the Congress of Racial Equality in 1962. The demonstration was staged to oppose housing segregation at the University of Chicago. It was Chicago's first civil rights sit-in.
Danny Lyon/Magnum Photos
Sanders takes the oath of office to become the mayor of Burlington, Vermont, in 1981. He ran as an independent and won the race by 10 votes.
Sanders takes the oath of office to become the mayor of Burlington, Vermont, in 1981. He ran as an independent and won the race by 10 votes.
Donna Light/AP
Sanders, right, tosses a baseball before a minor-league game in Vermont in 1984. US Sen. Patrick Leahy, center, was also on hand.
Sanders, right, tosses a baseball before a minor-league game in Vermont in 1984. US Sen. Patrick Leahy, center, was also on hand.
Toby Talbot/AP
In 1987, Sanders and a group of Vermont musicians recorded a spoken-word folk album. "We Shall Overcome" was first released as a cassette that sold about 600 copies. When Sanders entered the US presidential race in 2015, <a target="_blank">the album surged in online sales.</a> But at a CNN town hall, Sanders said, "It's the worst album ever recorded."
In 1987, Sanders and a group of Vermont musicians recorded a spoken-word folk album. "We Shall Overcome" was first released as a cassette that sold about 600 copies. When Sanders entered the US presidential race in 2015, the album surged in online sales. But at a CNN town hall, Sanders said, "It's the worst album ever recorded."
Toby Talbot/AP
Sanders reads mail at his campaign office in Burlington in 1990. He was running for the US House of Representatives after an unsuccessful bid in 1988.
Sanders reads mail at his campaign office in Burlington in 1990. He was running for the US House of Representatives after an unsuccessful bid in 1988.
Steve Liss/The LIFE Images Collection/Getty Images
In 1990, Sanders defeated US Rep. Peter Smith in the race for Vermont's lone House seat. He won by 16 percentage points.
In 1990, Sanders defeated US Rep. Peter Smith in the race for Vermont's lone House seat. He won by 16 percentage points.
Rob Swanson/AP
Sanders sits next to President Bill Clinton in 1993 before the Congressional Progressive Caucus held a meeting at the White House. Sanders co-founded the caucus in 1991 and served as its first chairman.
Sanders sits next to President Bill Clinton in 1993 before the Congressional Progressive Caucus held a meeting at the White House. Sanders co-founded the caucus in 1991 and served as its first chairman.
Marcy Nighswander/AP
Barack Obama, then a US senator, endorses Sanders' Senate bid at a rally in Burlington in 2006.
Barack Obama, then a US senator, endorses Sanders' Senate bid at a rally in Burlington in 2006.
TOBY TALBOT/AP
Sanders takes part in a swearing-in ceremony at the US Capitol in January 2007. He won his Senate seat with 65% of the vote.
Sanders takes part in a swearing-in ceremony at the US Capitol in January 2007. He won his Senate seat with 65% of the vote.
David Scull/Bloomberg/Getty Images
Sanders chats with Dr. John Matthew, director of The Health Center in Plainfield, Vermont, in May 2007. Sanders was in Plainfield to celebrate a new source of federal funding for The Health Center.
Sanders chats with Dr. John Matthew, director of The Health Center in Plainfield, Vermont, in May 2007. Sanders was in Plainfield to celebrate a new source of federal funding for The Health Center.
Toby Talbot/AP
Sanders speaks to reporters in 2010 about the Obama administration's push to extend Bush-era tax cuts. Three days later, Sanders held a filibuster against the reinstatement of the tax cuts. His speech, which lasted more than eight hours, was published in book form in 2011. It is called "The Speech: A Historic Filibuster on Corporate Greed and the Decline of Our Middle Class."
Sanders speaks to reporters in 2010 about the Obama administration's push to extend Bush-era tax cuts. Three days later, Sanders held a filibuster against the reinstatement of the tax cuts. His speech, which lasted more than eight hours, was published in book form in 2011. It is called "The Speech: A Historic Filibuster on Corporate Greed and the Decline of Our Middle Class."
Brendan Smialowski/Getty Images
Sanders and US Rep. Jeff Miller, chairman of the House Committee on Veterans' Affairs, walk to a news conference on Capitol Hill in 2014. Sanders was chairman of the Senate Committee on Veterans' Affairs.
Sanders and US Rep. Jeff Miller, chairman of the House Committee on Veterans' Affairs, walk to a news conference on Capitol Hill in 2014. Sanders was chairman of the Senate Committee on Veterans' Affairs.
J. Scott Applewhite/AP
In March 2015, Sanders speaks in front of letters and petitions asking Congress to reject proposed cuts to Social Security and Medicare.
In March 2015, Sanders speaks in front of letters and petitions asking Congress to reject proposed cuts to Social Security and Medicare.
Tom Williams/CQ Roll Call/AP
In July 2015, two months after announcing he would be seeking the Democratic Party's nomination for President, Sanders <a target="_blank">spoke to nearly 10,000 supporters</a> in Madison, Wisconsin. "Tonight we have made a little bit of history," he said. "You may know that some 25 candidates are running for President of the United States, but tonight we have more people at a meeting for a candidate for President of the United States than any other candidate has."
In July 2015, two months after announcing he would be seeking the Democratic Party's nomination for President, Sanders spoke to nearly 10,000 supporters in Madison, Wisconsin. "Tonight we have made a little bit of history," he said. "You may know that some 25 candidates are running for President of the United States, but tonight we have more people at a meeting for a candidate for President of the United States than any other candidate has."
Christopher Dilts/Bloomberg/Getty Images
Seconds after Sanders took the stage for a campaign rally in August 2015, a dozen protesters from Seattle's Black Lives Matter chapter <a target="_blank">jumped barricades and grabbed the microphone</a> from the senator. Holding a banner that said "Smash Racism," two of the protesters -- Marissa Johnson, left, and Mara Jacqueline Willaford -- began to address the crowd.
Seconds after Sanders took the stage for a campaign rally in August 2015, a dozen protesters from Seattle's Black Lives Matter chapter jumped barricades and grabbed the microphone from the senator. Holding a banner that said "Smash Racism," two of the protesters -- Marissa Johnson, left, and Mara Jacqueline Willaford -- began to address the crowd.
Elaine Thompson/AP
<a target="_blank">Sanders shakes hands with Hillary Clinton</a> at a Democratic debate in Las Vegas in October 2015. The hand shake came after Sanders' take on <a target="_blank">the Clinton email scandal.</a> "Let me say something that may not be great politics, but the secretary is right -- and that is that the American people are sick and tired of hearing about the damn emails," Sanders said. "Enough of the emails, let's talk about the real issues facing the United States of America."
Sanders shakes hands with Hillary Clinton at a Democratic debate in Las Vegas in October 2015. The hand shake came after Sanders' take on the Clinton email scandal. "Let me say something that may not be great politics, but the secretary is right -- and that is that the American people are sick and tired of hearing about the damn emails," Sanders said. "Enough of the emails, let's talk about the real issues facing the United States of America."
Lucy Nicholson/Reuters
Sanders embraces Remaz Abdelgader, a Muslim student, during an October 2015 event at George Mason University in Fairfax, Virginia. Asked what he would do about Islamophobia in the United States, Sanders said he was determined to fight racism and "build a nation in which we all stand together as one people."
Sanders embraces Remaz Abdelgader, a Muslim student, during an October 2015 event at George Mason University in Fairfax, Virginia. Asked what he would do about Islamophobia in the United States, Sanders said he was determined to fight racism and "build a nation in which we all stand together as one people."
Alex Wong/Getty Images
Sanders waves while walking in a Veterans Day parade in Lebanon, New Hampshire, in November 2015.
Sanders waves while walking in a Veterans Day parade in Lebanon, New Hampshire, in November 2015.
BRIAN SNYDER/REUTERS/Newscom
Sanders sits with rapper and activist Killer Mike at the Busy Bee Cafe in Atlanta in November 2015. That evening, Killer Mike <a target="_blank">introduced Sanders at a campaign event</a> in the city. "I'm talking about a revolutionary," the rapper told supporters. "In my heart of hearts, I truly believe that Sen. Bernie Sanders is the right man to lead this country."
Sanders sits with rapper and activist Killer Mike at the Busy Bee Cafe in Atlanta in November 2015. That evening, Killer Mike introduced Sanders at a campaign event in the city. "I'm talking about a revolutionary," the rapper told supporters. "In my heart of hearts, I truly believe that Sen. Bernie Sanders is the right man to lead this country."
David Goldman/AP
Comedian Larry David and Sanders <a target="_blank">appear together on "Saturday Night Live"</a> in February 2016. David had played Sanders in a series of sketches throughout the campaign season.
Comedian Larry David and Sanders appear together on "Saturday Night Live" in February 2016. David had played Sanders in a series of sketches throughout the campaign season.
Dana Edelson/NBC/NBCU Photo Bank/Getty Images
Sanders and his wife, Jane, wave to the crowd during a primary night rally in Concord, New Hampshire, in February 2016. Sanders defeated Clinton in the New Hampshire primary with 60% of the vote, becoming <a target="_blank">the first Jewish candidate to win a presidential primary.</a>
Sanders and his wife, Jane, wave to the crowd during a primary night rally in Concord, New Hampshire, in February 2016. Sanders defeated Clinton in the New Hampshire primary with 60% of the vote, becoming the first Jewish candidate to win a presidential primary.
John Minchillo/AP
Sanders speaks at a campaign rally in Ann Arbor, Michigan, in March 2016. He <a target="_blank">won the state's primary</a> the next day, an upset that delivered a sharp blow to Clinton's hopes of quickly securing the nomination.
Sanders speaks at a campaign rally in Ann Arbor, Michigan, in March 2016. He won the state's primary the next day, an upset that delivered a sharp blow to Clinton's hopes of quickly securing the nomination.
JIM YOUNG/REUTERS/Newscom
Sanders speaks at a campaign event in New York's Washington Square Park in April 2016.
Sanders speaks at a campaign event in New York's Washington Square Park in April 2016.
D Dipasupil/WireImage/Getty Images
Sanders speaks at a rally in Santa Monica, California, in June 2016. He pledged to stay in the Democratic race even though Clinton secured the delegates she needed to become the presumptive nominee.
Sanders speaks at a rally in Santa Monica, California, in June 2016. He pledged to stay in the Democratic race even though Clinton secured the delegates she needed to become the presumptive nominee.
John Locher/AP
Sanders <a target="_blank">endorses</a> Clinton at a rally in Portsmouth, New Hampshire, in July 2016.
Sanders endorses Clinton at a rally in Portsmouth, New Hampshire, in July 2016.
Taylor Hill/WireImage/Getty Images
Sanders <a target="_blank">addresses delegates</a> on the first day of the Democratic National Convention in July 2016.
Sanders addresses delegates on the first day of the Democratic National Convention in July 2016.
Anthony Behar/SIPA/AP
Sanders <a target="_blank">brings a giant printout of one of Donald Trump's tweets</a> to a Senate debate in January 2017. In the tweet, Trump had promised not to cut Social Security, Medicare and Medicaid.
Sanders brings a giant printout of one of Donald Trump's tweets to a Senate debate in January 2017. In the tweet, Trump had promised not to cut Social Security, Medicare and Medicaid.
Senate TV
Sanders thanks supporters after winning re-election to the Senate in November 2018.
Sanders thanks supporters after winning re-election to the Senate in November 2018.
Charles Krupa/AP
Sanders looks at his notes as he watches President Trump deliver the State of the Union address in February 2019. That month, Sanders announced that he would be running for president again.
Sanders looks at his notes as he watches President Trump deliver the State of the Union address in February 2019. That month, Sanders announced that he would be running for president again.
Win McNamee/Getty Images
Sanders hugs a young supporter during a campaign rally in Los Angeles in March 2019.
Sanders hugs a young supporter during a campaign rally in Los Angeles in March 2019.
Mario Tama/Getty Images
Sanders addresses the audience at a CNN town hall in Washington in April 2019.
Sanders addresses the audience at a CNN town hall in Washington in April 2019.
David Holloway for CNN
Sanders speaks next to former Vice President Joe Biden at the first Democratic debates in June 2019.
Sanders speaks next to former Vice President Joe Biden at the first Democratic debates in June 2019.
Drew Angerer/Getty Images
Sanders raises his fist as he holds a rally in Santa Monica, California, in July 2019.
Sanders raises his fist as he holds a rally in Santa Monica, California, in July 2019.
Damian Dovarganes/AP
Sanders grabs the hand of US Sen. Elizabeth Warren during the Democratic debates in Detroit in July 2019.
Sanders grabs the hand of US Sen. Elizabeth Warren during the Democratic debates in Detroit in July 2019.
Mark Peterson/Redux for CNN
Sanders campaigns at the University of New Hampshire in September 2019. A few days later, <a target="_blank">he took himself off the campaign trail</a> after doctors treated a blockage in one of his arteries. Sanders suffered a heart attack, his campaign confirmed.
Sanders campaigns at the University of New Hampshire in September 2019. A few days later, he took himself off the campaign trail after doctors treated a blockage in one of his arteries. Sanders suffered a heart attack, his campaign confirmed.
Preston Ehrler/SOPA Images/LightRocket/Getty Images
US Rep. Alexandria Ocasio-Cortez introduces Sanders at a New York rally after endorsing him for president in October 2019.
US Rep. Alexandria Ocasio-Cortez introduces Sanders at a New York rally after endorsing him for president in October 2019.
Mary Altaffer/AP
In a <a target="_blank">tense and dramatic exchange</a> moments after a Democratic debate, Warren accused Sanders of calling her a liar on national television. Sanders responded that it was Warren who called him a liar. Earlier in the debate, the two disagreed on whether Sanders told Warren, during a private dinner in 2018, that he didn't believe a woman could win the presidency.
In a tense and dramatic exchange moments after a Democratic debate, Warren accused Sanders of calling her a liar on national television. Sanders responded that it was Warren who called him a liar. Earlier in the debate, the two disagreed on whether Sanders told Warren, during a private dinner in 2018, that he didn't believe a woman could win the presidency.
Victor J. Blue for CNN
Sanders laughs during a primary-night rally in Manchester, New Hampshire, in February 2020. Sanders won <a target="_blank">the primary,</a> just as he did in 2016.
Sanders laughs during a primary-night rally in Manchester, New Hampshire, in February 2020. Sanders won the primary, just as he did in 2016.
Matt Rourke/AP
A triumphant Sanders raises his fist in San Antonio after he was projected to win <a target="_blank">the Nevada caucuses.</a>
A triumphant Sanders raises his fist in San Antonio after he was projected to win the Nevada caucuses.
Eric Gay/AP
Sanders and former Vice President Joe Biden talk before a Democratic debate in Charleston, South Carolina, in February 2020.
Sanders and former Vice President Joe Biden talk before a Democratic debate in Charleston, South Carolina, in February 2020.
Matt Rourke/AP
Sanders addresses supporters during a campaign rally in Grand Rapids, Michigan, in March 2020.
Sanders addresses supporters during a campaign rally in Grand Rapids, Michigan, in March 2020.
Jeff Kowalsky/AFP/Getty Images
Sanders speaks to reporters in Burlington, Vermont, a day after <a target="_blank">Super Tuesday II.</a> Sanders said it "was not a good night for our campaign from a delegate point of view" but that he looked forward to staying in the race and taking on Joe Biden in an upcoming debate.
Sanders speaks to reporters in Burlington, Vermont, a day after Super Tuesday II. Sanders said it "was not a good night for our campaign from a delegate point of view" but that he looked forward to staying in the race and taking on Joe Biden in an upcoming debate.
Charles Krupa/AP
Biden greets Sanders with an elbow bump before the start of a debate in Washington in March 2020. They went with an elbow bump instead of a handshake because of the coronavirus pandemic.
Biden greets Sanders with an elbow bump before the start of a debate in Washington in March 2020. They went with an elbow bump instead of a handshake because of the coronavirus pandemic.
Sarah Silbiger for CNN