It is a done deal. Obama by going to the UN and having the sanctions lifted bypassed Congress completely. Meaning whatever congress does from that point on is meaningless and is just a game of rhetoric and name calling. The Constitution states the senate must approve all treaties. By not calling this agreement a treaty, one should have known Obama at least in this case has made congress and the constitution meaningless. Of course he, the president has already done that numerous other times through EO's and failure to enforce the laws he and his administration don't like.
As for the agreement itself, only time will tell if it is good or bad. But it is a bad start to take congress's constitutional authority away from it. Has from this point on, whoever is president now become a king and congress just a relic of yore.
Unfortunately true. Ironically the Legislative Branch could take back its authority any time it wishes IF professional life time and corrupt to the bone politicians were consistently willing to risk everything fighting the Executive Branch (regardless of which Party's president holds it) to a standstill no matter what. But of course not enough from either party are ever willing to do that, and so they have pretty much politically neutered themselves.