It's all just symbolic on the part of the Legislative Branch because it's already a done deal and by the time that the LB could 'stop it' the mechanisms for giving Iran EVERYTHING it demanded of Obama and Kerry would already be done and probably could not be halted again -- or at least could not be halted in a meaningful way since the other nations that are signatories would not cooperate with putting the lid back on Iran.
So this posturing by the Legislative Branch is all sound and fury signifying . . . nothing. Effectively after Bush and now Obama the Legislative Branch essentially exists so that the president CAN point a trembling finger of blame somewhere AFTER he has screwed up big time. Sigh . . . and so it goes.
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.