There are still two way for Sanders to win the Democratic Nomination
Both scenarios are long shots, but they are real. Sanders did well enough last night by winning four contests to make scenario number one possible; which is an outright defeat of Hillary Clinton. For that to happen the campaign narrative needs to change significantly, and with it the momentum in the race.
Outside of the South, Hillary Clinton has had a had time putting Sanders away in any contest by anything approaching a resounding manner, and he has won most of them. Clinton's razor thin victory by about a quarter of one percent in Iowa barely counts; that falls well within the margin that triggers off an automatic recount in almost all normal elections. Hillary won clear but non decisive victories in Nevada and Massachusetts. Bernie won resounding victories in New Hampshire, Minnesota, Colorado, and Vermont, plus a strong ten point victory in Oklahoma.
The national campaign now starts to shift away from the South where Hillary Clinton has so clearly been dominant. There are four Democratic contests coming up this week before the primary in Michigan next Tuesday. Hillary can be expected to do extremely well in Louisiana, that is already baked in. The outcomes in Kansas, Nebraska and Maine are less certain, but there are reasons to think that Bernie can do well in all of them. There will also be another Democratic debate before the Michigan primary. If Bernie has a good week preceding the Michigan primary that contest becomes key to him.
Here is where the expectations game potentially shifts. Unlike with Super Tuesday, election night coverage next Tuesday won't literally be all over the map. On the Democratic side there will only be Michigan and Mississippi, and there is no mystery or intrigue concerning the latter. With an upset win in Michigan it may be possible for Sanders to leave that state having won four out of the last six Democratic contests, with the only exceptions being two deep South states no one gave him any prayer of winning. Not only that, but for Bernie to win in Michigan he will have had to demonstrably over performed current expectations of him. He will either have had to significantly decrease the percentage by which Hillary has been winning minority votes and/or strongly dominate the working class white vote and/or turn out the youth vote in much higher numbers than has generally been the case so far. None of that will be easy, which is precisely why it will instantly become very news worthy if Bernie Sanders wins in Michigan.
Obviously what determines who wins the Democratic nomination for President comes down to who wins the most delegates, not who has the best campaign narrative or the most momentum in mid March of 2016. But when the question is asked can Bernie Sanders still win the delegates he needs to become the nominee, the answer is yes. Not likely, but still definitely yes. If and when momentum strongly shifts, so does subsequent political reality. It is rare for momentum to swing back and forth like a pendulum, which is why whoever has it at this stage of a race usually builds on it and coasts to victory. That is why it seems so virtually impossible to many for Bernie Sanders to still turn this around, for him to win enough of the remaining states with big enough margins of victory to overtake the lead in delegates that Hillary Clinton now enjoys. But a scenario like the one I describe above is one that could open that window of opportunity for him.
The Clinton camp will deny that possibly vehemently. It is in their self interest to do so, to do so loudly, and to do so loudly repeatedly. Momentum, after all is ultimately an intangible that frequently spawns a self fulfilling prophesy. Based on current campaign dynamics, and the difficulty involved in altering those meaningfully, the odds do clearly favor Hillary Clinton winning the Democratic nomination for President. But there is a real factual basis for extrapolating how that can still change. And with a strong and passionate base of support and plenty of money in the bank, it is still possible for Bernie Sanders to do that. The seemingly improbable has happened before. Bernie Sanders has already shown that.
The second scenario is also a long shot, and I am not in any way arguing for it, but Hillary Clinton's campaign could still end up in serious difficulty if Hillary Clinton does herself, in regards to the FBI investigation of her emails etc. I really do not expect that to happen, but it is not beyond being conceivable. In the very unlikely event hat Hillary Clinton is forced to leave the race her delegates would then be up for grab in an open convention. If Bernie Sanders remains in this race and wins a considerable number of contests and delegate from here on out while doing so, it would become harder for the Democratic Party establishment to deny him the nomination by pushing for someone who didn't compete, say Joe Biden, instead. Under the circumstances it is prudent for Bernie Sanders to continue to actively contest the Democratic nomination throughout the full primary season.
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But I will simply add that this isn't the race most expected us to have prior to shortly before Iowa. I sure as hell didn't expect Bernie Sanders to have won five states against Hillary at this stage of the contest back when he first announced. 
