Electability will be the most important factor to Democratic voters when they watch Thursday night’s debate, argues E.J. Dionne in his latest column. He may be right that this will prove the decisive factor in the 2020 nomination battle, but it shouldn’t be.

To be sure, from the perspective of a Democrat, it’s understandable that choosing a candidate who can beat President Trump would be a priority. However, the problem is that voters have no real way of being able to predict who would match up best against Trump.