Senator Bernie Sanders ended his presidential bid, opening the way for former Vice-President Joe Biden to become candidate for the Democratic Party.
Mr Sanders, 78, told supporters on Wednesday that he did not see a viable way to win the nomination.
The Vermont senator, an early front runner, found traction with young voters but in recent weeks fell behind Mr Biden.
He also helped in making healthcare and wealth inequality important topics in elections.
During this year’s election cycle, among the most left-leaning candidates, the self-described “Democratic Socialist” campaigned on policies like health care for everyone, free public education, raising taxes on the rich and the minimum wage.
Mr Sanders, an Independent, had previously won the Democratic Presidential nomination, losing to Hillary Clinton in 2016.
He found favor with young voters in both elections who welcomed his calls for a democratic “revolution.”
He received a variety of celebrity endorsements including Cardi B, Ariana Grande, Miley Cyrus, Mark Ruffalo, and Dick Van Dyke.
Mr Sanders cemented his front-runner position with wins in New Hampshire and Nevada at the start of the Democratic primary election season 2020 but his momentum lagged later.
Mr Biden made a comeback by early March winning a number of big states, including Texas and North Carolina, and then racking up votes in Florida, Arizona and Illinois.
Mr Sanders failed to attract crucial African-American voters in the southern states, who went for Mr Biden to a significant degree.
Owing to health issues from the Covid-19 outbreak, Mr Sanders had been organizing campaign activities in recent weeks via live streams online.