Mr Sanders initially exceeded sky-high expectations about his ability to recreate the magic of his 2016 presidential bid, and even overcame a heart attack last October on the campaign trail.
But he found himself unable to convert unwavering support from progressives into a viable path to the nomination amid “electability” fears fueled by questions about whether his democratic socialist ideology would be palatable to general election voters.
Mr Sanders plans to talk to his supporters later on Wednesday.
The 78-year-old senator began his latest White House bid facing questions about whether he could win back the supporters who chose him four years ago as an insurgent alternative to the party establishment’s choice, Hillary Clinton.
Despite winning 22 states in 2016, there were no guarantees he’d be a major presidential contender this cycle, especially as the race’s oldest candidate.
However he used strong polling and solid fundraising - collected almost entirely from small donations made online - to more than quiet early doubters.
In a matter of days, his top former Democratic rivals lined up and announced their endorsement of Mr Biden.
The former vice president's campaign had appeared on the brink of collapse after New Hampshire but found new life as the rest of the party's more moderate establishment coalesced around him as an alternative to Mr Sanders.
He was also beaten in Missouri, Mississippi and Idaho the same night and the results were so decisive that Mr Sanders headed to Vermont without speaking to the media.
Mr Sanders had scheduled a rally in Ohio but cancelled it amid fears about the spread of coronavirus - and the outbreak kept him home as his campaign appeared unsure of its next move.
The senator addressed reporters the following day, but also sounded like a candidate who already knew he had been beaten.
"While our campaign has won the ideological debate, we are losing the debate over electability," Mr Sanders said then.