In other words, it's not the case that superdelegates are why Clinton is leading. But she does have a disproportionate lead among superdelegates, with The Post's tally suggesting that she has 469 superdelegates backing her to Sanders's 31. (Superdelegates can back whoever they want and change their minds at any time, as many did in 2008 as it became clear that Barack Obama would win the pledged delegate total that year.)
Since superdelegates make up 15 percent of the total delegate count for the Democrats, both Clinton and Sanders will need superdelegate votes in order to hit the 2,383 needed to clinch the nomination. Which has led some Sanders fans to question why superdelegates get to vote for whomever they want, instead of, say, having to back whoever won the state to which they're assigned.
We can look at how that changes the math fairly easily, since we know how many superdelegates there are in each state. In essence, some people want the superdelegates to act like winner-take-all statewide delegates, as exist on the Republican side. Part of the rationale for arguing that superdelegates should have to mirror the state is that Clinton's had a net win in terms of delegates in states that she lost thanks to superdelegates. In New Hampshire, for example, Sanders won six more pledged delegates -- but Clinton had six of the state's superdelegates.
But there's a problem with this line of thinking for Sanders's hopes at winning the nomination. And that is that applying the same rule to every state still means Clinton has more superdelegates so far.
In fact, even distributing the superdelegates from states that have already voted in a proportional way -- treating them like regular delegates, in other words -- Clinton still leads, although by less.
Which makes sense! After all, she has a wide lead because she won large states by big margins. Those large states had a lot of delegates and a lot of superdelegates. So mandating a way in which superdelegates have to vote doesn't really help Sanders much at all.
It's possible that Sanders could beat Clinton by 0.01 percentage points in every remaining state and then have more delegates in a superdelegates-all-go-to-the-winner-of-the-state scenario -- but it would still be close. If, however, Sanders were to somehow win the remaining states on the calendar by a wide margins, he would overtake Clinton's superdelegate lead under a proportional system.
But that's what he needs to do anyway! The easiest way to win the nomination is always to win the most pledged delegates. In 2008, superdelegates ended up backing Barack Obama in part because he proved that he was going to win among pledged delegates. (That we're comparing 2016 and 2008 is in itself remarkable and not something that the would have predicted a year ago, of course.)
One line of thinking among Sanders supporters appears to be that his "momentum" from winning late states will force the superdelegates to change their minds, which requires ignoring the states that voted earlier. It requires, in other words, the superdelegates undermining the will of the voters.
Which is precisely what many of his supporters appear to fear.
* The RealClearPolitics polling margins are as follows. New York: Clinton, +13.7. California: Clinton, +9.5. Pennsylvania: Clinton, +16. Maryland: Clinton, +24. RCP doesn't have an average for New Jersey yet, but a Rutgers-Eagleton poll from February had Clinton up 23.