In 2016, Bernie Sanders ran a bootstrapped campaign on small-dollar donations and a vision of a political revolution to transform the country in a manner not seen since the 1930s. And he did change the Democratic Party dramatically, not only pushing the party to the left but powering an overhaul of the rules that dethroned the traditional party power brokers who, he felt, put their thumbs on the scales for Hillary Clinton.

So why could his 2020 campaign put those same brokers back in the saddle?

The answer requires a dive into the way three recent changes to primary campaigns are likely to interact with 2020's big field: the rise of small-dollar fundraising, the front-loading of big-state primaries, and the proportional allocation of delegates.

Historically, one way that large fields like 2020's get winnowed down is that fundraising dries up. Big donors don't want to waste their money on a hopeless campaign, and they are generally well-appraised of which campaigns are hopeless.

But the campaign phenomena of recent years — like Sanders' 2016 presidential run or Beto O'Rourke's 2018 Senate run in Texas — were powered more by small-dollar donations than by old-school bundlers. Those donations, in turn, were driven by social media more than any other communications tool — which means they could bypass traditional media gatekeepers who might pour cold water on a campaign unlikely to win.

What all that means is that a long-shot campaign can stay in the game a lot longer, so long as their supporters believe in it. But how long can believers keep their faith?

That's where the schedule comes in. Because of the primary schedule, supporters don't need to stay committed very long to have a profound impact on the outcome. The first contest in 2020 is the Iowa caucuses on Feb. 3. Within a month, thirteen states representing a third of pledged delegates will have voted — including the mega-states of Texas and California. It's extremely unlikely that candidates like California's Kamala Harris or, if he runs, O'Rourke will drop out before Super Tuesday, when their home-state advantage could put them over the top — particularly when early voting may mean a lot of people cast their ballots before they learn how their favored candidate did in earlier contests.

With a large number of candidates coming into Super Tuesday, it's unlikely any one of them will dominate completely. But because pledged delegates are allocated proportionally to the vote, it's also unlikely any of them will get a majority, even if they win a number of contests. Harris, for example, could win California with 35 percent of the vote, and get only 35 percent of California's delegates, with Sanders, Warren, Klobuchar, Booker, and (if they run) Biden and O'Rourke taking various-sized bites out of the rest. And California is likely to be her best state. If enough viable candidates stay in through Super Tuesday, it's entirely possible that no candidate will have won more than 25 percent of the pledged delegates up for grabs. Recall, for comparison, that Donald Trump, who was the overwhelming poll leader all through the primary season, won only about a third of the votes cast on Super Tuesday.

Of course, the field will eventually narrow, after Super Tuesday, if not before. Candidates who are overwhelming long shots will be pressured to leave for the good of the party, which will want to rally around a frontrunner — or at least allow a clear frontrunner to amass a majority of delegates. If Cory Booker, Amy Klobuchar or Kirsten Gillibrand hasn't caught fire by then, they'll surely bow out.

But there's one candidate who party leaders can't pressure to get out of the race. And whether he's leading or lagging, he could make it extremely difficult for any candidate — including him — to cobble together a majority of pledged delegates.

If Sanders has amassed a delegate plurality by Super Tuesday, of course, there will be huge pressure from the left for the party to unite behind him. But Sanders still has a lot of opposition in the party, both from those who resent and distrust him as an outsider and those who oppose his agenda. They'll be unlikely simply to acquiesce and back Sanders, particularly if his plurality is relatively small. If there is at least one other viable candidate — and there surely will be in such a diverse and fractured field — it's likely the contest will continue.

But if his plurality through Super Tuesday is as little as 25 percent, then to amass a majority would require Sanders to win a supermajority of the remaining delegates — perhaps as many as two-thirds. Could Sanders consolidate the party behind him that quickly? And of course, the path to a majority for a candidate already behind in the delegate count would be even tougher.

Moreover, that path gets steeper very quickly. In the two weeks after Super Tuesday, states representing over 20 percent of the total pledged delegates will vote, including Midwestern mammoths like Michigan, Missouri, Ohio, and Illinois, along with the megastate of Florida. By March 17, states representing well over a majority of pledged delegates will have voted. If no candidate has more than a third of those delegates in hand — which is where the leader hypothetically would be if he or she won 25 percent of the delegates through Super Tuesday and roughly half the delegates in the two weeks thereafter — they'd need to win nearly three quarters of the remaining delegates to earn a majority. And because of the proportional allocation of delegates, to get those delegates they'd need three quarters of the votes.

That wouldn't be impossible in a normal contest. John Kerry's dominance after Super Tuesday in 2004 was overwhelming — he lost only North Carolina, and racked up margins of greater than 70 percent in states like Florida, Illinois, Pennsylvania, and Oregon. But consolidation has proven distinctly difficult for Democrats in recent years — and could prove difficult again. Even if Sanders had only gotten 15 percent or 20 percent of the delegates through Super Tuesday, if the delegate leader wasn't that far ahead of him he could consolidate the anti-establishment vote and deny the delegate leader a majority by taking a quarter to a third of the vote through the convention. And if we saw a replay of either 2008 or 2016, where after the party had already decided, an opponent (Clinton and Sanders, respectively) with enthusiastic backing not only refused to leave the field but gained strength down the stretch, then consolidating a majority would be impossible for any candidate.

What happens then? Ironically, the rules changes Sanders fought for could give the party leadership more explicit power than ever. Under the new rules, unpledged "super delegates" cannot vote on the first ballot. Pledged delegates have to vote for their pledged nominee. So if no candidate has consolidated a majority in the primaries, then the first ballot will not yield a nominee. And after that first ballot, pledged delegates are unbound and unpledged delegates can vote. It's an old-time brokered convention — the dream of all political reporters.

Is such a scenario likely? No. The field could winnow substantially before the very first votes are cast. Biden could run and suddenly dominate the field — or collapse and leave the field open to Sanders. The debates could prove decisive, deflating the balloon of an O'Rourke or a Castro and boosting a level-headed former prosecutor like Klobuchar. Warren could win Iowa and New Hampshire and run the table from there on. Anything — except Howard Schultz winning the nomination — is still possible.

But it's much more likely with Sanders in the race than not. If Sanders can't complete his revolution in the primaries, he'll have every reason to take it to the convention, and play his hand with party leaders in a smoke-filled room. And because they know it, those same leaders will have a powerful incentive to bring Sanders' revolution indoors before the primaries are over, if only to preserve the appearance that the voters have decided.