﻿Bernie Sanders, the progressive whose two campaigns for president pulled the Democratic Party to the left, ended his White House bid Wednesday, leaving former Vice President Joe Biden as the party’s presumptive nominee for the 2020 election.

The Vermont senator’s announcement created fresh urgency for Mr. Biden to unite the factions within the party and win over Mr. Sanders’s supporters. It also capped a remarkable turnaround for the former vice president and a stark fall for Mr. Sanders, who was the front-runner after the first three nominating contests, before Mr. Biden’s decisive victory in South Carolina vaulted him into a series of triumphs in early March and a nearly insurmountable delegate lead.

Mr. Sanders, 78 years old, ended his bid following Tuesday’s Wisconsin primary, which was marred by logistical and political challenges that could face voters in November if the pandemic lingers. During a live stream address, Mr. Sanders acknowledged that his “path toward victory is virtually impossible,” adding that if he “had a feasible path to the nomination, I would certainly continue the campaign. But it’s just not there.”

Mr. Sanders said the coronavirus pandemic, which kept him from holding his signature massive rallies, was a critical factor in his decision to leave the race. And while Wisconsin will not report results until next week, polling indicated he was likely to suffer another significant loss.

A senior aide to Mr. Sanders said his decision was the culmination of weeks of discussions and evaluation of different scenarios. His campaign had expected Wisconsin, like many other states, to postpone its primary, the aide said, giving him more time for consideration. But after the Supreme Court ruled the election would proceed, the urgency for Mr. Sanders to make a decision increased.