With their center’s collapse, Democrats’ only hope of reconstituting it is by redefining the center. As the Democratic primary race moves leftward, the definitions of their candidates are moving right. It resembles a play in which we are expected to accept that the same actors have become different characters simply because of a costume change. When the 2020 Democratic field was taking shape a year ago, its spread was straightforward. Former Vice President Joe Biden was the establishment anchor, in a center-left, front-runner position. A couple of candidates were to his right – Montana Gov. Steve Bullock and former Rep....