It wasn’t a treaty the last time around.
Exactly. Obama basically circumvented the constitutional requirement for Senate ratification by declaring that it was not a treaty, even though it was.
Of course you live by the sword you die by the sword and thus Trump could immediately rescind the executive orders that implemented the deal.
There are some benefit to consulting key Senators of both parties to secure ratification but that’s not the Democrat way anymore. Damn the torpedoes and steamroll the opposition.