With three losses on Tuesday night, Bernie Sanders’s chances of winning the Democratic presidential nomination became even slimmer.

The defeats in Arizona, Florida and Illinois left even some of the Vermont senator’s top staffers frustrated and questioning whether he should continue his campaign.

One campaign senior adviser told Yahoo News it was time for Sanders to begin winding down his campaign.

“The time has come for some true reflection for this campaign,” the senior Sanders adviser said, adding, “Tonight is hard, and it’s also time for some hard decisions.”

Sanders’s exit would leave former Vice President Joe Biden, who won in all three states that voted on Tuesday, as the presumptive Democratic presidential nominee.

Another senior Sanders aide expressed frustration over a lack of direction from the campaign’s top leadership: campaign manager Faiz Shakir, the senator’s longtime confidant Jeff Weaver and Sanders himself.

The senior aide indicated that concerns were exacerbated by the fact that Biden now has an almost insurmountable lead in delegates. The aide compared Sanders to Tulsi Gabbard, the congresswoman from Hawaii, who is continuing her presidential bid although she has only won two delegates and never attained more than single digits in national polls.

“It’s clear there is no plan,” the senior Sanders aide said. “It feels like we’re doing a Tulsi Gabbard.”

The situation is reminiscent of the 2016 presidential primary, when Sanders continued to run even after he fell well behind former Secretary of State Hillary Clinton in the delegate count. Sanders’s decision to remain in that race also frustrated some of his team.

Sen. Bernie Sanders, I-Vt., arrives to speak to reporters on March 12, in Burlington, Vt. (Charles Krupa/AP)

However, this year is also far different. Unlike in 2016, Sanders has spent time in this race as a frontrunner with a clear path forward, while Biden’s campaign was on the ropes. Sanders performed well in the first three states that voted. He won the popular vote in Iowa, got a win in New Hampshire, and scored a large victory in Nevada.

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But on Feb. 29, Biden began to turn things around, with a rout in the South Carolina primary. Biden’s triumph came with a series of endorsements from the Democrats who had dropped their own presidential bids. The momentum propelled him to a strong performance in the slate of Super Tuesday votes on March 3.

Since then, Sanders has framed the race as an opportunity to contrast his policy vision with Biden's. But while he has pledged to support Biden once the race is over, Sanders has not given in to the growing gulf in the delegate race.

The abrupt turnaround from frontrunner to long shot is particularly frustrating for the members of Sanders’s team, since many of them feel that he was treated unfairly by the “political establishment” the senator so often rails against.

Moments that particularly rankled Sanders and his allies included the delayed reporting of results in Iowa and high-volume media coverage of Biden’s South Carolina win.

Sanders and his allies also felt they were mounting an uphill battle against the Democratic Party and the media in 2016. However, this time, those frustrations are compounded by the fact that the coronavirus pandemic has effectively brought an abrupt end to the presidential primary.

Former Vice President Joe Biden and Sen. Bernie Sanders before their debate in Washington on March 15. (AP Photo/Evan Vucci)

Voting was also scheduled to take place in Ohio on Tuesday night, but Ohio Gov. Mike DeWine postponed the primary there until June 2, citing safety issues posed by the coronavirus.

Both Sanders and Biden have canceled a slew of live campaign events since March 10. And while some on Sanders’s team feel that the coronavirus has eclipsed the primary and slammed the door shut on his candidacy, they also feel that it raised awareness around a central issue of his platform: the lack of affordable public health care in the United States.

One senior Sanders campaign source who is aware of the senator’s conversations about his future plans described this time in the campaign as an “unprecedented moment.”

“History tells us we can’t trust the political establishment in a time of crisis to look out for working people and low-income people,” the senior campaign source said, adding, “We’re going through a viral pandemic that could kill hundreds of thousands of Americans. Right now, Bernie Sanders has the largest, most powerful progressive platform in the country. … To describe this moment as uncharted would be an understatement.”

Another senior Sanders adviser expressed frustration that more states didn’t delay voting and that the Democratic National Committee had issued a statement calling for the primary to proceed on schedule. The adviser suggested that the difficulty voters might face leaving their homes amid the contagion could cloud the results and blamed the DNC for “playing politics” by calling for the race to continue.

The adviser also lamented that it was difficult for Sanders's allies to raise these problems without being portrayed as sore losers, rather than being viewed as concerned about public health.

“I feel frustrated because people are literally either physically dying or losing their livelihood, yet the DNC … played politics with the pandemic, and our campaign could not really tell people what to do one way or the other,” the senior adviser said. “Because if we do that, then it seems as though we are deliberately trying to postpone the primary for some political reasons, when the real reason is: We actually give a damn about people.”

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