Senator Bernie Sanders of Vermont is dropping out of the Democratic presidential race on Wednesday, concluding a quest for the White House that began five years ago in relative obscurity but ultimately elevated him as a champion of the working class, a standard-bearer of American liberalism and the leader of a self-styled political revolution.

Mr. Sanders’s exit from the race establishes former Vice President Joseph R. Biden Jr. as the presumptive nominee to challenge President Trump, and leaves the progressive movement without a prominent voice in the 2020 race.

In a race reshaped, and eclipsed, by the escalating coronavirus crisis, Mr. Sanders faced no realistic path to the nomination after a series of lopsided losses to Mr. Biden, beginning in South Carolina in late February and culminating with a string of losses last month in crucial states like Michigan and Florida.