Bernie Sanders’s interview with the New York Daily News last month was proof to some that he had little mastery of policy. Hillary Clinton warned voters that Sanders “had [problems] answering questions about even his core issue, breaking up the banks.”

Clinton-sympathetic voices in the media echoed her concerns; Sanders supporters defended their candidate.

It might be tempting to write off the exchange as just more partisan bickering. But it raised a question that has been persistent throughout this election season.