One senior adviser to Bernie Sanders delivered a blunt assessment of Tuesday night’s primary results.

“The godd*** plane has crashed into the mountain,” the adviser told Yahoo News.

Just two weeks ago, Sanders — who earned the most votes in Iowa, New Hampshire and Nevada — was the prohibitive favorite to secure the Democratic presidential nomination.

But after likely victories by a resurgent Joe Biden in most of the states that voted Tuesday (including the big delegate prize of Michigan), the question now facing Sanders isn’t whether he’s going to win the Democratic primary.

The question is how he decides to lose.

Barring some sort of dramatic, unforeseeable upheaval, the Vermont senator’s chances of topping the Democratic ticket dwindled from slim to nonexistent on Tuesday. And with that vanishing window of opportunity comes a choice.

In 2016, Sanders frustrated even some of his staff and allies as he continued to campaign against rival Hillary Clinton long after it became clear he couldn’t win the nomination, remaining in the race through June and declining to officially endorse Clinton until two weeks before that summer’s Democratic National Convention.

So does Sanders run the same play he ran in 2016? Or does he start to search for a quicker, most unifying exit?

Even before Tuesday, Sanders indicated that he was not inclined to defy the delegate math and soldier on indefinitely.

“I’m not a masochist who wants to stay in a race that can’t be won,” Sanders told ABC News’ George Stephanopoulos on Sunday. “But right now, that’s a little bit premature. Let’s not determine what will happen on Tuesday and what will happen in the future.”

Now that Tuesday has happened, however — and now that it didn’t go as Sanders had hoped — the decision about how to proceed is upon him. While his devoted supporters will likely push him to keep running forever, there are three reasons to think Sanders might pursue a less combative path than in 2016 — and perhaps even drop out and endorse Biden sooner rather than later.

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Joe Biden, accompanied by his wife, Jill, speaks at the National Constitution Center in Philadelphia on Tuesday after his primary wins. (Matt Rourke/AP)

The first reason Sanders could soon stand down is that Democratic superdelegates — elected officials and party leaders who are automatically seated at the convention — hold much less sway this time around. In 2016, superdelegates were allowed to declare their candidate preference during the primaries and vote on the first ballot in Philadelphia, which not only gave Clinton a head start in the overall delegate count but put her over the top at the convention. Trailing Clinton by hundreds of pledged delegates and unable to reach a majority himself, Sanders spent much of the second half of the 2016 contest lobbying superdelegates to switch sides and back him over Clinton.

But going forward, Sanders won’t have that excuse for remaining in the race. Because of a rule change demanded by his own campaign, superdelegates now don’t get to vote until the second ballot in Milwaukee — that is, only if no candidate secures a majority of pledged delegates in the primaries. And Sanders has already said that whoever arrives at the convention with the most delegates “should become the nominee.”

“If Biden walks into the convention, or at the end of the process, has more votes than me, he’s the winner,” Sanders told MSNBC host Rachel Maddow in an interview Wednesday.

“And that’s true whether or not he has a majority or a plurality [of delegates]?” Maddow asked.

“Absolutely,” Sanders said.

While Sanders doesn’t have to be bound by that declaration, changing his position would come across as crassly opportunistic.

The second reason Sanders might not overstay his welcome is that Donald Trump, who was the underdog in 2016, is now the incumbent, and every poll says that ending his presidency is the most important thing to Democratic voters. In 2016, when few seemed to think Trump could actually win the White House, the stakes of a drawn-out Democratic primary battle seemed lower. That logic no longer applies, so Democrats are unlikely to tolerate another lost-cause crusade that could weaken their nominee in November.

The third reason Bernie could concede earlier than 2016 is Biden himself. Unlike Hillary Clinton, the former vice president has never been a particularly formidable frontrunner. He has stumbled frequently on the debate stage. He has struggled to raise money. His campaign infrastructure is small and wobbly. Part of Sanders’s calculation in 2016 was that Clinton was strong enough to withstand his continuing challenge — and that she might even become a better candidate by having to battle him down to the wire. Biden seems more vulnerable. That may influence Sanders’s decision about how long and how hard to go after him.

“At the end of the day, I have known Joe Biden for a very long time,” Sanders said Sunday on ABC News." “He is a decent guy. I have no doubt that if I win, Joe will be there. If Joe ends up winning, I will be there. We are going to come together.”

Sen. Bernie Sanders outside a polling location in Detroit on Tuesday. (Paul Sancya/AP)

As Sanders looks ahead, a primary concern is whether he would have more leverage for his policy agenda in the race or out of it.

Sanders has focused his presidential bids on sweeping calls for universal health care, free public education and other measures to reduce income inequality. Biden is set to secure the nomination after pitching himself as a more moderate alternative to Sanders on each of these fronts.

A senior Sanders aide said Biden would do well to adopt elements of Sanders's platform.

“To have the best chance of defeating Trump, the Democratic Party must have a nominee who makes explicitly clear that they are on the side of Medicare for All, not the insurance companies; on the side of Social Security, not the billionaires who want to cut it; and on the side of workers, not the CEOs who want to pass new trade deals that sell workers out,” said the senior Sanders aide.

If he chooses to continue his campaign, the road ahead for Sanders would be daunting (as we noted elsewhere). Before Tuesday’s primaries and caucuses, Biden led the Vermont senator by nearly 100 delegates; now he leads Sanders by more.

Meanwhile, Biden’s national polling lead has skyrocketed; as of Tuesday, he was trouncing Sanders by nearly 20 points, with a majority of Democratic primary voters (roughly 52 percent) saying they support him. That may be the most rapid polling swing in presidential primary history: a gain of roughly 35 points in just 14 days.

The calendar isn’t doing Sanders any favors, either. Next Tuesday, four big states — Arizona, Florida, Illinois and Ohio — will vote; Georgia votes the Tuesday after that. The latest polling averages show Biden ahead by wide margins everywhere: 37 points in Florida, 29 points in Ohio, 21 points in Arizona; 24 points in Illinois and 34 points in Georgia.

The first one-on-one Democratic debate will take place Sunday in Phoenix, and Sanders was banking on a knockout performance to reset the race.

“I can’t imagine him dropping out without getting his chance to get this guy one on one in a debate,” a senior Sanders aide told Politico.

But given that Florida and Arizona both rely heavily on early voting, even a sterling display might prove to be too little, too late.

Sanders's position is especially perilous in light of what follows: the so-called Acela primary on April 28, when voters in Connecticut, Delaware, Maryland, New York, Pennsylvania and Rhode Island go to the polls. Named after Amtrak’s higher-speed northeastern rail line, it’s the second-biggest day of primary season, with 663 delegates at stake — and perhaps the single most favorable one for Biden, who was born and raised in Pennsylvania; who represented Delaware in the U.S. Senate for 36 years; and who may be Amtrak’s most famous passenger.

And even if the schedule weren’t so stacked against Sanders, history would still be on Biden’s side. No modern presidential candidate has ever mounted a successful comeback after Super Tuesday (or the equivalent point in the race). The reasons are simple: winning begets winning, and fewer and fewer delegates are available for the lagging candidate to close the gap.

Twelve years ago — post-Super Tuesday — Barack Obama's lead in the national polls was a third the size of Biden’s today. Four years ago, Hillary Clinton’s lead was half the size of Biden’s. Neither of their challengers — Clinton in 2008 and Sanders in 2016 — was able to catch up.

For Sanders, that makes a comeback even less likely than it was in 2016.

“If our projections thru 3/17 (next Tuesday) are right, the delegate count at that time would be Biden 1317, Sanders 992, other 139, with 1531 pledged delegates unallocated,” data journalist Nate Silver tweeted Monday. “Sanders would then have to win 65 percent of remaining delegates to earn a majority, which is roughly equivalent to beating Biden by 30 points” — with big, Biden-friendly states such as Georgia, Pennsylvania, New Jersey and Maryland still to come.

In other words, after losing big this week and next, Sanders would need a sudden polling swing much larger than the record-shattering reversal that has boosted Biden since his resounding win in South Carolina on Feb. 29 — something on the order of 50 percentage points.

Unless Sanders thinks he can pull off that improbable feat — and quickly — he will soon have to start weighing his other options.

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