Here's how Trump voters gave Bernie Sanders a boost in West Virginia

You know who may have helped pull Bernie Sanders over the top to victory in Tuesday’s West Virginia primary? Donald Trump voters, that’s who. 

That’s what exit poll data from NBC indicates, in any case. About one-third of the West Virginia Democrats who cast ballots on Tuesday say they plan to vote for Mr. Trump in November, according to NBC’s data. By a wide margin those voters picked Senator Sanders over Hillary Clinton.

Here’s where it gets really weird: fully 39 percent of Sanders’s supporters said they would vote for Trump over Sanders in a hypothetical general election matchup. Thirty-nine percent! They’d just voted for Bernie but really they liked somebody else better? 

West Virginia has open primaries so it is possible that some Republicans crossed over to vote for Sanders as a means to sabotage front-runner Mrs. Clinton. Plus, exit poll data can be a bit squirrelly.

But what’s likely behind this strange number is West Virginia’s political history. Unlike other Southern and border states it has not completely finished the transition from Democratic control to GOP dominance sparked by the ideological and racial upheaval of the 1960s and '70s.

Fifty-one percent of West Virginia’s registered voters are Democrats. But many are DINOs – Democrats In Name Only. They’re conservative and generally vote GOP.

“The thing to know about West Virginia: huge numbers of registered Dems who are conservative, vote Republican in presidential elections,” tweeted New York Times Upshot poll guru Nate Cohn on Tuesday.

That would explain why Sanders, the liberal alternative to Clinton, won self-described conservatives in the state, according to NBC’s data.

Barack Obama is particularly unpopular in West Virginia. In 2012 Mitt Romney won the state by 62 to 36 percent. (Remember, the state’s voter registration is majority Democrat. But Mr. Obama? Hammered.)

“That seems to have damaged Clinton, his former cabinet member who is running to continue his legacy,” writes NBC’s Alex Seitz-Wald.

The only other state with a similar mismatch between party identification and partisan behavior is Oklahoma. That means Trump voters are unlikely to play a big role in the Democratic race, per se.

The case of West Virginia does illustrate the larger point that Sanders supporters tend to have completely different political identities than Clinton counterparts. To oversimplify, Sanders depends heavily on self-identified independents who lean Democratic. He’s one himself, having only joined the party just prior to his presidential run. Clinton is the candidate of the party regulars, the registered Democrats who have long been comfortable with the “D” word.

That’s why Sanders does better in states with open votes, where anyone can vote in any primary they choose. Clinton does better in primaries closed to Democratic voters.

Will this be a problem in the general election? Probably not. The ideological and political differences between stereotypical Sanders and Clinton voters aren’t nearly as large as those between Trump supporters and the GOP establishment.

But some disappointed Bernie supporters may stay home. And in modern American elections, marginal changes can make a difference. Just ask President Al Gore.