I've been loath to estimate the relative chances of Secretary Clinton and Senator Sanders to win the nomination, though the odds favor Clinton, who leads in pledged delegates. The question that interested me is to determine how voters' opinions must change if Sanders is to win. I made a few simplifying assumptions: (a) Among likely Democratic voters, Clinton leads Sanders 52% to 48%, (b) Clinton has an additional edge in New York (4%), Maryland (4%), Indiana (5%), West Virginia (5%), Kentucky (5%), and the District of Columbia (18%), (c) Sanders has an additional edge in Oregon (10%), Montana 5%), and New Mexico (5%), and (d) pledged delegates will be awarded exactly proportionately to the vote. I also assumed that Senator Sanders will not attract enough superdelegates to win unless he defeats Secretary Clinton in the race for pledged delegates by a margin of at least 200, i.e., the superdelegates will stick with Secretary Clinton unless Sanders defeats her by a wide margin, but that if the margin is wide enough, they will change.
Taking today's pledged-delegate totals of 1,307 for Clinton and 1,097 for Sanders, with 1,647 yet to be chosen, means that Senator Sanders needs to win 1,029 of the remaining pledged delegates.
I then added an assumption that for each remaining week of the campaign, there will be some flow of voter support from Clinton to Sanders, and then meshed this with the primary schedule, meaning that, other things being equal, Sanders will do better in the two primaries that are four weeks away than he will in one of tomorrow's three primaries, because the voters in the two later states have more time to be persuaded to change their minds. A little fiddling with a spreadsheet reveals that, on these assumptions, each week Sanders must attract 7.5% of Clinton's supporters to change their minds, net of any flow in the opposite direction, in order to win 1,029 pledged delegates. )"Attracting 7.5% of her supporters" translates to a shift of 3.75% of the voters in a state in which Clinton and Sanders are tied.)
What might we learn from tomorrow's primaries? In my model, Clinton will receive 56% of the New York vote and 52% in Connecticut and Delaware. If she wins only 52% of the New York vote, Sanders's task doesn't become much easier. Sanders still has to attract 7.2% of her supporters each week to get to 1,029 more pledged delegates. If Secretary Clinton has the 4% edge in New York that I'm crediting her with, but she and Sanders are tied nationally, Sanders must attract 6.8% of her supporters each week to get to 1,029 delegates, including winning 64% of the California vote. That's a lot of votes to change in seven weeks.
The first test of my model will be next week, in the primaries for Maryland, Pennsylvania, and Rhode Island, and in comparing those results with tomorrow's results in Connecticut and Delaware. New York is its own beast.