Let's remember that the US is not the world's "decider". The Iran Nuclear Agreement was negotiated by six parties, US, UK, France, Russia, China and Iran. Furthermore, just recently the 15 members of the U.N. Security Council voted unanimously in Favor of the Iran deal. That's a lot of international opinion unequivacally in favor of the Iran nuclear agreement. OK let's suppose the US Congress voted against the deal and then overode the President's veto, in effect quashing the agreement. Somehow, I don't think the rest of world minus Israel will be particularly enthusiastic about continuing the sanctions nor in treating Iran as the outcast nation in as much as Iran was willing to abide by a negotiated agreement promising not to build a nuclear weapon. I think the international sentiment will be fairly pissed off at the US for poisoning the well of negotiations. If some future Republican president thinks he'll be able to negotiate a better agreement he's kidding himself.