Bernie Sanders, a democratic socialist whose progressive agenda pushed the Democratic Party sharply to the left, ended his White House campaign overnight, clearing the way for a 3 November election battle between former Vice President Joe Biden and Republican President Donald Trump.
Senator Sanders, a one-time front-runner who promised to lead a grassroots political revolution into the White House, acknowledged he no longer had a path to victory after a string of decisive nomination contest losses to Mr Biden but promised to work with his more moderate former rival to oust Mr Trump.
The independent US senator from Vermont said the coronavirus outbreak, which has taken him off the campaign trail and limited his ability to get his message out, required a broad response and urgent attention in Congress.
"I cannot in good conscience continue to mount a campaign that cannot win, and which would interfere with the important work required of all of us in this difficult hour," he said in a live-streamed speech to supporters from his hometown of Burlington, Vermont.

Senator Sanders described his decision as "difficult and painful." Source: AAP
Senator Sanders, 78, called it a "difficult and painful decision" but said he would stay on the ballot in future primaries and continue to gather delegates in order to push the Democratic platform toward his populist anti-corporate agenda, including a government-run healthcare system and tax hikes for the rich.
The departure of Senator Sanders, Mr Biden's last remaining rival in a field that once included more than two dozen candidates, sets up a long battle for the White House between the 77-year-old Mr Biden and Mr Trump, 73, who is seeking a second four-year term in office.
That matchup for the foreseeable future will revolve around Mr Trump's handling of the public health crisis that has upended all aspects of American life and rocked the country's economy.

With Senator Sanders stepping down, it clears the way for former Vice-President Joe Biden to become the Democratic party's nominee. Source: AAP
Mr Biden on Wednesday signaled he was ready for a bruising general election fight and the challenge he now faces in trying to unite the Democratic Party's liberal and moderate wings.
"It's going to be a really rough and I suspect pretty mean campaign," Mr Biden told donors at an online fundraising event after Senator Sanders' announcement.
In a separate statement, he praised Mr Sanders and promised his ideas would be incorporated into Mr Biden's White House run.
"I see you, I hear you, and I understand the urgency of what it is we have to get done in this country," Mr Biden said to Senator Sanders' supporters. "I hope you will join us. You are more than welcome. You’re needed."