The explanation likely would come down to some version of “everybody knows.” Everybody knows that Sanders is gaining ground fast even with minority voters who had been for Joe Biden. Everybody knows about polls suggesting he is up comfortably in the nation-state of California, and is going to emerge from Super Tuesday a week from now with an enormous delegate lead. Everybody knows there is no way to deny him the nomination if he goes into the July convention in first place, even if not enough for a first-ballot majority.

It’s not our place to tell everybody they are wrong. We aren’t sure they are. But it is fair to remind people that what everybody knows has been wrong before, including in the very recent past. And there are some big reasons it may not be right this time.

Let’s examine some of the reasons to say “not so fast” in assuming that Sanders’ impressive momentum coming out of the Nevada caucuses makes him unstoppable.

Debates matter—sometimes

To underline the obvious, tonight’s televised encounter in Charleston, South Carolina could be a very big deal. Sanders has sparred with rivals plenty over the past year but has never been the target of sustained, break-glass-in-emergency attacks. That is almost certainly going to change.

He can expect criticism on his record and past comments on Cuba, guns, the Soviet Union, his promises on health care and the state of his own health — you name it, a barrage that likely will start early and not let up.

Across nine previous encounters, Sanders has been the most consistent debater on stage. The variance between his best performances and his weakest has been narrow. This will be a critical test of whether it will still work simply to bark gruffly with old talking points as he faces new and detailed criticism of his record and relevant questions about his electoral prospects against President Donald Trump.

In the early debates, there was plenty of faux drama over now-forgotten viral moments. The last couple occasions, however, the drama has been real. Amy Klobuchar got a clear bounce out of a strong New Hampshire debate a couple weeks ago, and Elizabeth Warren likely did in Nevada. At a minimum, Mike Bloomberg’s weak performance in Las Vegas caused his national numbers to swoon.

Sanders’ perceived juggernaut status could look very different a few hours from now.

Biden’s firewall holds

So much of the former vice president’s coverage has been about under-performance — fourth place in Iowa, fifth in New Hampshire, second in Nevada — that it may be discounting the effect of something he has long promised: A South Carolina victory with a majority of African-Americans backing him.

For this to come true it would mean that polling-based speculation that Sanders and billionaire Tom Steyer are gaining among minority voters in South Carolina would turn out to be hype. Weak performances with minority voters among Steyer, Klobuchar, and Pete Buttigieg would produce enormous pressure on them to depart the race either before or immediately after Super Tuesday on March 3.

In short, if Biden can for once exceed expectations with a decisive South Carolina showing the Democratic contest suddenly look quite different.

The Audacity of Nope

Here’s something “everybody knows” that is almost certainly true. The two most widely respected figures in the Democratic Party — Barack Obama and Nancy Pelosi — are worried that a Sanders nomination could be disastrous for the party in the fall, increasing the likelihood that Trump is reelected or that enough marginal House Democrats lose their seats to turn congressional control back to the GOP.

Of course, the reason an outsider like Trump took over the Republican Party is the same reason a socialist like Sanders might take over the Democratic Party: Party leaders simply do not wield the same levers of power in an era of online ideological movements.

But that doesn’t mean they have no leverage. Obama, in particular, would not necessarily need to launch a full-on campaign against Sanders to signal misgivings, either with his own voice or through surrogates that people would know are authorized by him. He could remind African-American voters that Sanders wants to repeal and replace Obamacare, and that the Vermont senator considered a primary challenge to Obama’s reelection in 2012. The message: A vote for Bernie is akin to a repudiation of the Obama legacy.

Revenge of the Superdelegates

The assumption that the Democratic National Convention couldn’t dare deny the nomination to Sanders if he has a first-round plurality deserves some skepticism.

Under 2020 rules, superdelegates do not even get to vote in the first round of convention balloting unless a candidate already has a first-round majority. The whole rationale for super-delegates is that they get to assert their voice in the event the primaries are inconclusive.

What’s more, these superdelegates are not Wall Street bankers or even wine cave habitués. Many of them are African-American party regulars, including elected officials, who prize their votes and have been deeply resistant to efforts to neuter their influence. They aren’t likely to be intimidated by the protests of predominately white “Bernie Bros.”

Imagine that Sanders comes into the convention with a weak plurality, far short of 1,991 delegates. When he asserts that the candidate with the most delegates should be awarded the delegation, and rails against the establishment, he is confronted with his comments from 2016 like this one.

“The responsibility that superdelegates have is to decide what is best for this country and what is best for the Democratic Party,” Sanders said. “And if those superdelegates conclude that Bernie Sanders is the best candidate, the strongest candidate to defeat Trump and anybody else, yes, I would very much welcome their support.”

His brand is suddenly tarnished – he looks like every other self-serving politician.

A fluid race means a fluid race

Sanders’ support among his partisans has been perhaps the most stable factor in the race so far. If anything, a heart attack last fall probably had the effect of energizing supporters.

Think of all the other factors — including the consensus about what everybody knows — that have been constantly in flux.

Recall the widespread assumptions that Biden is stronger than people think when weak debate performances didn’t much affect his national polling; that Warren is the likely nominee on the basis of her polling numbers last fall; that Buttigieg was potentially an Obama-style insurgent upending the system on the basis of his Iowa support; that Bloomberg was demonstrating the fearsome power of money and advertising on the basis of his polling before the most recent debate.

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The wheel is likely to keep spinning. Bloomberg’s money and arguments about electability could yet be a factor — it might not take much more than a strong debate tonight. The fact that so many candidates remain in the race — in an earlier era many more would have already dropped out, unable to sustain themselves with online contributions — is a reminder that old assumptions are defunct.

That means surprises keep happening. Perhaps the biggest surprise would be if the prevailing wisdom about the current trajectory of the race turned out to be substantially correct.