Is Bernie Sanders really going to be the Democrats' presidential nominee?

It may seem strange for me to highlight any doubts on that score. Sanders has already achieved something no prior candidate ever has — he won the popular vote in each of the first three contests — and his margin of victory has only increased with each state. But while Sanders is the clear leader in national polls and delegate accumulation, he's still a long way from putting the nomination to bed. And the odds of nobody winning a majority of delegates — rated at 42 percent by the folks at FiveThirtyEight — may actually still be underestimated.

We now have a number of polls from Super Tuesday states and beyond that reflect Sanders' strong victory in Nevada, as well as Mike Bloomberg's dismal debate performance in Las Vegas. And they tell a very mixed story about the upcoming contests.

On the one hand, Sanders is way ahead in California, polling in the mid-30s against a very fragmented field where most of his competition doesn't clear the 15 percent threshold for getting delegates. There hasn't been much if any recent polling of Colorado, Utah, Vermont, and Maine, but based on demographic factors alone Sanders would be favored to win each of those states by comfortable margins.

But beyond those states, the picture is much murkier — and much less-favorable to Sanders. Biden leads or ties for the lead in the two most recent polls of North Carolina. He also leads in the most recent poll of Oklahoma, as well as Missouri, which votes after Super Tuesday but whose demographics make it useful for predicting states like Arkansas and Tennessee that haven't been polled recently. Those polls are especially remarkable given that Biden has been largely absent from the airwaves, and has had no really positive headlines, while Sanders has racked up three straight wins and Bloomberg has been bombarding these states with ads.

There is a very plausible world, in other words, in which Biden wins South Carolina and goes on to win at least five and perhaps as many as seven additional Southern and border states on Super Tuesday. Who's the frontrunner then?

It depends. Because of the proportional allocation of delegates, it matters a great deal who comes in second or third, and how well they perform.

In recent polling of California, Elizabeth Warren is in second place and rising — and polling strongly enough that she has a good chance of earning a respectable share of the delegates. Even a quarter of California's 415 delegates would be worth more than the entire delegate slate from Warren's home state of Massachusetts. A win there coupled with a strong second in California and a smattering of delegates from Colorado, Texas, and elsewhere might be enough for Warren to believe that she could wield some influence at the convention.

In the Southern and border states where Biden looks strongest, meanwhile, his closest competition is as likely to be Bloomberg as Sanders. In the most recent polls, Bloomberg runs a strong second in Oklahoma and Missouri, and he was tied for the lead in one North Carolina poll while rating a strong third in the other. If he is able to convert those polls into votes, Bloomberg could take a real bite out of Biden's delegate haul even if he wins not a single state.

The most recent polling of Texas and Virginia is particularly striking, for those are the states where the Super Tuesday narrative is likely to be decided. In a post-Nevada poll from Public Policy Polling, Biden and Sanders were tied for the lead in Texas, with Bloomberg a strong third and Warren nipping at Bloomberg's heels. Without Bloomberg in the race, Biden would have a clear lead, and Warren would be a closer third behind Sanders. In Virginia, the last pre-Nevada poll had Bloomberg tied with Sanders for first place, with Biden close behind, and while a new poll shows the state turning sharply in Sanders' direction, a Biden win in South Carolina could well tip the scales back again.

A very realistic scenario after Super Tuesday, then, looks something like this. Sanders is the clear delegate leader; a big haul from California makes that almost certain, particularly given that he should earn delegates in states across the South even if he comes in third. But he might have won fewer states than Biden, and no states outside of the West and Northeast. While Biden may have won more states, though, and states worth more delegates in aggregate than those Sanders won, a strong Bloomberg showing could mean that his actual delegate haul is relatively modest, maybe as little as half of what Sanders brings home. And if Warren performs strongly in California and Massachusetts, and Klobuchar wins her home state of Minnesota, no candidate may have accumulated more than a third of the total delegates allocated.

What happens then? It's hard to say.

Since the Democratic Party may resist coalescing around a registered independent like Sanders and Bloomberg will never have to drop out of the race for lack of funds, a three-way or even four-, five- or six-way contest could well continue to play out well past March 3. In that case, the calendar isn't going to settle anything.

Sanders would be favored to win Michigan and Washington, the two biggest delegate prizes on March 10. But he would be expected to lose badly in Missouri and Mississippi. On March 17, Sanders would likely lose Florida — a poor state for him even before his comments on Castro and AIPAC made headlines, and one of Bloomberg's best states. But he can't be assured to win either Illinois or Ohio, both of which have characteristics that make them plausible wins for Biden, especially if he had done well on Super Tuesday. Sanders could expect to win Wisconsin and Oregon, but lose Louisiana and Georgia to Biden. And then come New York, Pennsylvania, and New Jersey, all states where either Biden or Bloomberg could potentially outpace him. Sanders could mop up delegates in a number of smaller states, like New Mexico and Rhode Island, along the way — but he could also lose smaller states, like Kentucky, where the demographics are less-favorable to his coalition.

A true nightmare scenario is all too possible: Sanders limps into Milwaukee as the clear delegate leader, well ahead of Biden and Bloomberg, but with well under 40 percent of the delegates, having lost the entire South, including Texas, Florida, and Virginia, much of the Northeast and Mid-Atlantic, including Pennsylvania and Massachusetts, and half of the Midwest. That outcome would be the worst possible result for the Democratic Party, which would have to choose between anointing an extraordinarily weak nominee or essentially invalidating the primaries.

I can think of only two plausible ways such an outcome could be averted: if either Sanders breaks through or Biden consolidates.

Sanders could break through on Super Tuesday with a decisive win in Texas. Even one win in a somewhat-Southern state would make Sanders the only candidate with truly national support. And as Texas is the second-largest delegate prize of the day, and the third-largest of the entire primary season, the victory would make it all but impossible for Biden to spin a scenario that he is actually the frontrunner. The fact that Sanders went to El Paso immediately after Nevada and then barnstormed across the state strongly suggests his campaign concurs about the vital importance of Texas. The task of the national party, in that circumstance, would be to make it clear that even if Sanders isn't their preferred nominee, he will have the party's support if he wins, and that there will be no organized effort by the party to stop him. The odds are that such a message would lead to natural consolidation by voters in later primaries around the clearly-leading candidate.

Biden could consolidate by sweeping the South, and denying Bloomberg any victories on Super Tuesday. At that point, there would be no plausible path forward for Bloomberg to come in first or second in the delegate haul, to say nothing of Warren, Buttigieg, or Klobuchar. If the party wants the voters to decide, they should want the race to quickly narrow to a two-person contest at that point. They can make that happen simply by declaring that the convention is not going to be wide open. Either the delegate leader is going to be the nominee, or the laggards are going to be expected to align their support with one of the leaders in what would effectively be a ranked-choice vote by proxy. That should foreclose the possibility of Bloomberg buying the nomination, giving him a strong incentive to stand down, and leave it to Sanders and Biden to contest the remaining states through Milwaukee.

The party doesn't have to decide — the voters can and should. But the party needs to decide, and soon, how they are going to satisfy the voters that they have been heard, so that they can come together at the convention and not tear the party apart.

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