It seems almost too obvious to mention, but presidential candidates need a clear idea of why they want to be president. In the past few days, Democrats have heard that their still-undeclared frontrunner, Hillary Clinton, needs time to think about the question. Meanwhile, another undeclared hopeful, Elizabeth Warren, is thrilling liberal audiences with a forceful, point-by-point declaration of the principles that would guide her as president. The contrast is striking.

Clinton is offering Democrats her resume. Warren is offering them a plan.