He also made gestures toward Mr. Sanders and his loyal base of liberal supporters, saying: “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.’’
Mr. Sanders, 78, leaves the campaign having almost single-handedly moved the Democratic Party to the left. He inspired the modern progressive movement with his expansive policy agenda and his impassioned message that “health care is a human right,” and electrified a legion of loyal supporters who wholeheartedly embraced his promise to lift up those who need it most. He also transformed the way Democratic campaigns raised money, eschewing big fund-raisers and instead relying on an army of small-dollar donors.
But Mr. Sanders stirred deep unease among party leaders, and as he ascended to the top of the field in February, establishment Democrats scrambled to block his path, convinced his far-reaching proposals would alienate great swaths of the electorate and make him an easy target for Mr. Trump.
Moderate candidates in the race who could not overcome Mr. Biden dropped out and endorsed the former vice president just before Super Tuesday, on March 3, helping him sweep 10 of 14 states on the biggest voting day of the primary. That led to a wave of new endorsements and a remarkable coalescing around Mr. Biden that Mr. Sanders could not match on the left.
And while Mr. Sanders burst onto the political scene in 2015 as an insurgent populist, he no longer benefited from being the only alternative to an establishment he couldn’t stand. He also faced a formidable rival in Mr. Biden, who was competing for white working-class voters, a critical slice of Mr. Sanders’s constituency.
Even before Mr. Sanders announced in February 2019 that he was running again, there were indications his campaign would not be smooth. His media consulting team abruptly quit after clashing with him and his wife, Jane, over an announcement ad. Through the spring, he largely stuck to his familiar message, battling establishment forces rather than his immediate rivals. Amid a slump in the polls in the fall, he suffered a heart attack while campaigning in Las Vegas, a startling event that threatened to upend his bid.
The health crisis prompted even some of his allies to call for him to drop out and endorse his ideological ally, Senator Elizabeth Warren of Massachusetts.