The 2020 presidential campaign will begin all too soon, alas, and one question is whether Democrats nominate a centrist or someone from the rising left wing. The chances of the latter rose Saturday when the Democratic National Committee changed its rules to strip superdelegates of their first-ballot nominating leverage.
Superdelegates are party officeholders and insiders who in 2016 represented about 15% of nominating delegates. Most favored Hillary Clinton, and they were her backstop had Bernie Sanders won enough delegates…