The battle for the Democratic nomination is almost over, but the battle to define the meaning of the Bernie Sanders campaign has just begun.

Does the Vermont socialist’s improbable success — fueled by historic levels of support from younger voters — herald the rise of a new left-wing bloc in American politics? Or is the Sanders phenomenon closer to a passing fad, little more than a protest vote against Hillary Clinton?

Writing in the New York Times, political scientists Christopher Achen and Larry Bartels recently joined the debate.