Cohen was merely exercising the Left's favorite tactics:
1. Eschew discussion of policy and attack the opponent's intelligence and character.
2. Whenever possible, accuse the opponent of your own sins.
3. Escalate the vilification to the point that matters of fact and historical precedent cannot be heard.
4. Above all, discourage the audience from investigating the opponent's actual contentions.
Were it not for these -- and gratuitous screams of "RACISM!" -- the Left would be without any weapons at all.