What debate was there?

He's referring to the point that if the JCPOA was indefensibly ass because Iran is Iran and thus can never be constrained by a deal, then that means that the deal that Trump is currently trying to negotiate will also be indefensibly ass, no matter what the terms are. Because Iran will still be Iran. So any deal that relies on Iran agreeing to constraints is indefensibly ass, because Iran will always have the desire and capability to cheat, no matter the terms or the inspection/enforcement protocol.

If this war ends in Iranian promises, rather than the overthrow of the regime, I assume we can count on you to attack whatever that deal is as "indefensibly ass" on the same grounds that Iran has a history of noncompliance and therefore it is wishcasting to believe they would ever comply with this new agreement?