In 2008, Democratic nomination contenders Barack Obama and Hillary Clinton tore each other to shreds. Some of it was political and substantive while some of it was personal and slimy. But none of it would be considered “civil” by the standards now being applied to today’s Democratic primary.

It’s not a coincidence that the right flank of the party started finger-wagging about divisiveness, incivility, and disunity precisely when the left flank began to seriously threaten its dominance. As the left wing gains momentum, the party establishment’s tolerance for legitimate criticism wears thinner, and the range of topics considered off-limits or below-the-belt expands. New behavioral norms have appeared out of thin air: suddenly political criticisms of opponents, no matter how legitimate by traditional standards, are a bridge too far, and are even alleged to help Donald Trump. At least, if the criticisms are flying from left to right.

It should be obvious that all the scolding about divisiveness is merely a reflexive defense mechanism, an easier task for centrists than defending their politics on its merits. It deserves little more consideration than that. But if we do decide to subject to closer scrutiny the idea that criticism in a primary imperils the winner’s prospects in the general election, we find that it quickly falls apart.