WASHINGTON (Reuters) - Bernie Sanders is reassessing his White House bid after bruising losses to Joe Biden in the latest Democratic presidential nominating contests, a senior adviser said on Wednesday, as the campaign suspended its political advertising on Facebook.

Sanders, a U.S. senator from Vermont who less than four weeks ago appeared to have the inside track on winning the Democratic Party’s nod to take on Republican President Donald Trump in November, is facing increasing pressure to abandon his campaign as Biden has emerged as the clear front-runner.

The former vice president’s dominating victories in Florida, Illinois and Arizona on Tuesday effectively closed off any viable path for Sanders, even as the coronavirus outbreak seems likely to force the candidates to remain off the campaign trail for weeks, or maybe months, to come.

“The next primary contest is at least three weeks away. Sen. Sanders is going to be having conversations with supporters to assess his campaign,” his campaign manager, Faiz Shakir, said in a statement.

The campaign’s decision to pull Facebook ads was part of “conserving resources,” according to Sanders’ communications director, Mike Casca.

On Tuesday night, Biden made a direct appeal to Sanders’ base of young backers, as he turned his attention to Trump and the general election.

“Senator Sanders and his supporters have brought remarkable passion and tenacity to these issues, and together, they have shifted the fundamental conversation in the country,” Biden said.

Democratic U.S. presidential candidate Senator Bernie Sanders speaks during the 11th Democratic candidates debate of the 2020 U.S. presidential campaign, held in CNN's Washington studios without an audience because of the global coronavirus pandemic, in Washington, U.S., March 15, 2020. REUTERS/Kevin Lamarque/File Photo

“And let me say, especially to the young voters who have been inspired by Senator Sanders: I hear you. I know what is at stake. And I know what we have to do.”

AVOIDING A 2016 REPEAT

Many Democrats are worried about a repeat of the bruising primary battle that Sanders and eventual nominee Hillary Clinton waged in 2016. But some Sanders allies have urged him to campaign through the primaries, even if he can’t win, to give him more leverage to influence the party’s platform at the convention.

Sanders, a democratic socialist whose sweeping agenda would reshape the American economy, was leading the race as recently as the last week of February, after a dominating performance in Nevada’s caucuses.

Biden’s campaign, meanwhile, was on life support following underwhelming finishes in the early voting states of Iowa and New Hampshire, as centrist voters split their support among several rivals.

But the moderate Biden’s commanding win in South Carolina on Feb. 29, powered by African-American voters, pushed other candidates, such as Senator Amy Klobuchar of Minnesota and former South Bend, Indiana, Mayor Pete Buttigieg, to drop out and endorse him. Since then, Biden’s momentum has only accelerated.

His latest wins have given him a nearly insurmountable lead over Sanders of 971 to 737 delegates to the Democratic National Convention in July, according to Edison Research. A candidate needs 1,991 delegates to clinch the nomination.

Sanders, 78, has struggled to expand his coalition of supporters, while his vow to increase turnout among infrequent voters has thus far not succeeded. The coronavirus outbreak has also prevented him from holding rallies.

Nevertheless, Biden, 77, still faces work to persuade Sanders’ backers to support him against Trump, 73, particularly young voters. Voters between the ages of 18 and 44 were the only major demographic to stick with Sanders on Tuesday, Edison Research polls showed.

The Democratic nominating campaign begins an extended hiatus on Wednesday, after concerns about the coronavirus outbreak prompted several states to postpone their contests, including Ohio on Tuesday. The only primary election scheduled between Wednesday and April 4 is in Puerto Rico, where lawmakers appeared poised to delay the vote until late April.

Hours after saying Sanders would weigh his options, campaign aides were forced to deny a report by Axios news - later withdrawn - that he was ending his campaign. A corrected article reported the decision to end Facebook advertising.

GRAPHIC-Calendar of Democratic nominating contests and state delegates - here

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GRAPHIC-Where the candidates stand on key issues - here