Watching panicky corporate-owned Democrats twist on the devil's fork of Bernie Sanders' "political revolution" is almost as much fun as it must have been for my mom and her fellow villagers to watch Vichy collaborators and Nazi sympathizers being executed by the resistance at the end of World War II. (That, Chris Matthews, is how you do a Nazi-to-2020 metaphor.)
Centrist/moderate/Third Way Dems are afraid of Sanders, not because he would lose to Trump or inverse-coattail down-ballot candidates, but because they would lose their long-standing minority control of the party apparatus. After the convention in Milwaukee, for example, the nominee gets to choose the new Democratic National Convention chairman. Sanders will not keep Tom Perez.
Electability, however, is the moderates' supposed chief concern. And enough moderate Democratic voters are buying it to make it a thing.