Sanders' campaign manager, Faiz Shakir, and senior adviser, Jeff Weaver, have likewise declined to answer questions from POLITICO about what his path looks like. While it’s not yet mathematically impossible for him to win, Sanders would need to amass more than 60 percent of the remaining delegates to clinch the nomination — a mark he’s only hit in two states this year, Nevada and his home state of Vermont.

His path is so narrow that some of Sanders' senior aides have even advised him to consider dropping out, though not everyone in his inner circle feels the same way, according to people familiar with the situation.

Another possible reason for not explaining his long-shot course to victory: it depends on something his staff and allies have for the most part only whispered about — an epic Biden collapse. But his remarks also suggest that Sanders could decide to remain in the race even absent a path in hopes of tugging Biden to the left, a task many progressives see as even more critical amid the coronavirus pandemic and economic meltdown.

“He knows he has a mathematical path if he starts to win these primaries, and they’re primaries he’s won before in 2016,” said Larry Cohen, chairman of the Sanders-founded group Our Revolution, who has known Sanders for nearly 30 years. “But he always knows that he is the leader of the progressive Democrats and there’s millions of them left to vote and delegate count matters in terms of leverage.”

Sanders hinted at an alternative rationale for staying in the race on Friday, when he said on MSNBC that “the key goal is obviously to win, but the other goal is to be able to continue to fight to give people the opportunity to participate in the political process to stand up for the views that they believe in.”

In recent weeks, Sanders and his campaign have been speaking with his allies about what he should do next. Sanders acknowledged this week that “among my supporters, there are different points of view as to how we should proceed.” His staff likewise privately voice divergent opinions.

According to people familiar with his thinking, Sanders often agonizes over big choices, and he may still be coming to terms with the fact that he likely cannot take the nomination despite coming tantalizingly close earlier this year, they said.

“I just think he’s in his rumination phase. When he makes a decision, he ruminates and ruminates and ruminates, and gets enormously wrapped up in his head,” said a Democrat who has known Sanders for years. “It feels to me like that’s where he is: He’s sort of rolling it over.”

Many of Sanders’ allies have openly admitted that Biden is all but guaranteed to be the nominee. Still, some are urging him to stay in the race in order to collect delegates for the Democratic National Convention, which was pushed back to August because of the pandemic.

It is especially important to these Sanders supporters to maintain the rule changes they achieved in 2016, such as barring superdelegates from voting for presidential candidates on the first ballot. In order for his backers to have negotiating power, they said, Sanders needs to receive at least 1,200 delegates — he has more than 900 now — so they can introduce minority resolutions. They also hope that Sanders can push Biden to commit to progressive appointments.

“The party reforms go down the drain if he doesn’t stay in,” said Cohen, adding that if he drops out before hitting 1,200 delegates, "it’s going to be Biden’s people writing the platform, that’s it."

In recent weeks, Sanders has retooled much of his campaign to focus on the coronavirus and workers’ rights — both markings of a candidate running a message candidacy rather than a true race against Biden. He has raised more than $3.5 million for coronavirus aid, while ceasing to actively raise money for himself. He has also used his email list and social media accounts to drive up support for Walmart and Amazon employees fighting for protective equipment and additional benefits during the pandemic.

But managing even a successful message campaign at this moment could prove difficult, given that the coronavirus death toll and response efforts are commanding nearly all of the media’s attention. Last weekend, CNN and ABC canceled tentative appearances with Sanders.

Despite how bad his prospects for victory look, some of Sanders’ allies and former aides argue that an upset is not out of the realm of possibility, especially in these catastrophic times — providing a window into at least some of Bernieworld’s thinking as he remains in the race.

The fact that moderates and conservatives are entertaining ideas such as free coronavirus treatment — combined with the fact that Sanders won Wisconsin in 2016, and Medicare for All’s popularity has risen to a nine-month high in a recent Morning Consult-Politico poll — is giving them a shred of hope.

“I'm pretty confident that he's going to do very well in Wisconsin,” said Randy Bryce, the co-chair of Sanders' campaign in the state. “He won 71 of 72 counties in 2016.”

But the respected Marquette Law School survey released this week found that a lot has changed since Sanders defeated Hillary Clinton there by double digits in 2016: Sanders now trails Biden by a whopping 28 percentage points. Regardless, some of Sanders’ allies continue to speculate that Biden could seriously stumble, giving him a reason to stay in the race.

“The path to someone else getting the nomination besides Joe Biden is Joe Biden on television, and Joe Biden exposing himself as a weak candidate. I’m hopeful that the Democratic Party will come to its senses and nominate Bernie Sanders,” said Kurt Ehrenberg, Sanders’ former longtime political strategist in New Hampshire. “It’s clear to people who look at it that the health care system is failing us when we need it most. Who else has been hearkening us to this problem in such an articulate and smart way?”

Asked whether it is harmful to the progressive cause for Sanders to lose to Biden by double digits in state after state, Ehrenberg said no. “At this point, numbers don’t matter. It’s the fight that matters. It’s what Bernie has always done well, which is lead the fight.”

Sanders has not advertised online or on television, and cannot hold his trademark large rallies due to the coronavirus. But despite his long odds, Sanders continues to quietly campaign in Wisconsin.

His volunteers and staffers have made more than 300,000 calls to remind voters in the state to request absentee ballots, with 1,000-plus of them participating in the outreach to residents in the last week and a half alone, an aide said. Sanders also has upwards of 50 staffers dedicated to Wisconsin, including a state coordinator, field director and political director.

Whether Sanders is campaigning in Wisconsin to lead the progressive fight — or believes he can still actually win the nomination — is a separate question.