A POLITICO analysis underscores Sanders’ challenge: Even after runaway victories in Idaho, Utah, Alaska, Hawaii and Washington this week – he still trails Clinton by between 200 and 250 pledged delegates, pending final tallies from this week’s races. And while Wisconsin’s April 5 primary and Wyoming’s April 9 caucuses seem well-suited for the Vermont senator, the Democrats’ proportional delegate-allocation rules limit the extent to which he can eat into Clinton’s advantage.

Looking forward past the next two weeks, he currently trails Clinton in public polling in the four largest states left on the calendar: California, New Jersey, New York and Pennsylvania. With the exception of his win in Michigan earlier this month, Sanders hasn’t yet demonstrated he can win large states like these – let alone by the wide margins he’ll need to close the pledged-delegate gap.

Another problem for Sanders: He has excelled in caucus states – winning 10 of 12 (including the last 10 consecutively). But most of the states left to come are holding primaries, including a number of contests only open to registered Democrats.

And Clinton has another insurance policy: the more than 700 so-called “superdelegates” who can support the candidate of their choosing on the convention floor, regardless of the primary or caucus results in their home states.