Something that’s essentially been said but maybe not succinctly:
On Tuesday Sanders need to reduce his delegate margin from Hillary down from 225 (225 as of Today, Clinton won the Northern Marianas 4-2 delegates) to some number lower than 225. At the end of the day Tuesday 49.8% (let’s call it half) of all delegates in the primary will have been allocated. So it would no longer be the case that “it’s still so early, so many states haven’t voted etc”, because we’ll be on the “downward slope” after Tuesday. Mathematically that means that for the second half of the primaries to have any chance of swinging the election to Bernie he needs a smaller margin between him and Hillary.
If he wins “Michigan style”, Missouri, Illinois and Ohio but Hillary wins Florida by the estimated amount, he would still lose margin–and likely that’s when it’s very hard to not consider him mathematically eliminated. The media will be talking about who won which State on Tuesday, as “educated observers” watch the delegates, if that margin stays at 225 or higher, then it doesn’t matter who won what state, the race is over.
I just plotted out a projection where Bernie wins every state but Florida roughly similar to how he won Michigan (so I give him 51.5% of the delegates from those states, using standard rounding rules and giving Hillary the remainders.) That creates splits like this:
Illinois: 80/76 +4 Margin
Missouri: 37/34 +3 Margin
North Carolina: 55-52 +3 Margin
Ohio: 74/69 +5 Margin
Total Margin from Wins: 15
Then I estimated Hillary wins Florida with 58% of the vote (the 538 projection is she wins it with 68% of the vote, so I’m docking her 10 points):
Florida: 124/90 +34 margin
So she goes up 19 more delegates in the margins, and Bernie now trails by 244, and he needs to win 56% of all delegates remaining. That means he has to beat Hillary by 12% in 29 straight elections. Including places like Maryland with very high black populations, or New York where she was a Senator, and the Appalachian states which are rural and white but which supported Hillary tremendously versus Obama in 2008 (i.e., we don’t know if they’re going to look more like Oklahoma or more like the South.) If he won even one of those states by say, 5%, then his numbers for the other 28 have to be higher. If she wins even one, the numbers higher still. That’s how a “delegate squeeze” works, he not only has to win, he has to win by large margins, in every election.
Note this above scenario is pretty generous. It assumes in the four open primaries that day, in three of them Bernie has polling upsets about the same as those in Michigan–which have been called historic. Several of these states also have things going against Sanders, like early voting (so a late swing to him will be less impactful) and some like North Carolina or Ohio have pretty good economies. Ohio is a rust belt state like Michigan, but has actually been able to do pretty well economically (Trump says it’s because of fracking, which hasn’t hurt, but a lot of it is also that Ohio just has a more diversified economy, a large educated work force, and a lot of major corporations are headquartered there, it’s also a transportation hub for the eastern United States.)
It also assumes in Florida, where you had to pre-register as a Democrat 29 days before Tuesday, that has high numbers of non-whites, that has a somewhat older electorate than the norm, that Sanders still takes Hillary down from the 68% she’s polling to 58%–even doing that he loses margin.