Bernie Sanders won the West Virginia primary on Tuesday night, setting back Hillary Clinton's efforts to turn to the general election against Donald Trump.
Clinton has amassed a big delegate and popular vote lead and is still overwhelmingly likely to be the Democratic nominee. Tonight's results won't change that.
But Sanders's drubbing of Clinton — which follows similarly large wins for the Vermont senator in Oklahoma, Kansas, and Nebraska — has important implications for Bernie's ability to fight for his platform ahead of the Democratic convention.
Clinton is almost certainly going to be the nominee
Bernie Sanders needs one of two things to happen to secure the nomination, and neither is likely:
1) Sanders wins more pledged delegates than Clinton
Sanders could still win more of the pledged delegates — those chosen by the voters at the ballot box — than Hillary Clinton. But to do so, he'll need to take the remaining states with margins nobody expects to be possible.
Going into tonight, Clinton had 1,707 pledged delegates to Sanders's 1,408 — a difference of about 300. There are 926 of these pledged delegates left in the remaining 12 contests, which you might look at and reasonably conclude Sanders still has a shot. It's certainly not mathematically impossible. (To put tonight in perspective: Only 29 delegates were on the table in West Virginia.)
The problem is that because of the Democrats' proportional allocation rules, a candidate has to win by a huge margin among the voters to cut into an opponent's delegate advantage.
Sanders is going to have to win 65 percent of the remaining delegates to catch Clinton's pledged delegate lead. And for that to happen, he will need to make up huge margins in his current polling gaps in remaining states like New Jersey and California, which command the lion's share of the remaining delegates.
Part of the problem for Sanders is the Democrats' proportional allocation rules, which mean a candidate needs to win by huge margins to cut into his or her opponent's lead.
"Proportional allocation of delegates makes comebacks really, really hard. You can’t just notch wins in a string of states, as Sanders did in late March and early April," writes Milo Beckman at FiveThirtyEight. "You have to start consistently trouncing your opponent by large margins in every contest."
This may sound unfair, but the rules work both ways. If we were judging by popular vote alone, Sanders might face even longer odds — Clinton has gotten more than 2 million more votes than Sanders, even factoring for the vote share in the caucuses Sanders won, according to the Washington Post.
2) Convincing the superdelegates to overturn the will of the voters
The other way Sanders can still win the nomination is by persuading the unelected superdelegates to override the will of the voters and give him the nomination.
For reasons I explained here, this outcome is also very unlikely to happen — the superdelegates are Democratic loyalists who have been with Clinton since the start of the campaign. But that's not stopping Sanders from appealing to them to save his candidacy.