If you think the 2016 presidential campaign is already wild, imagine where we’d be without Democratic superdelegates. Bernie Sanders might be the next President.

The 74-year-old socialist won West Virginia’s primary on Tuesday, his 19th victory and second in a row. He still trails Hillary Clinton 1,719 to 1,425 in bound delegates, by CNN’s count, but he’s won a majority of the delegates since March 1. If he sweeps the final 10 primaries and caucuses, he might take the lead among bound delegates heading into the Democratic...