IRAN NUCLEAR WEAPON AGREEMENT VOTE

A vote on the Iran Nuclear Weapon agreement is coming up soon.  This is a pretty important issue, with plenty of risk for the future whether the agreement is ratified or rejected.  The first point, that I think is not being discussed, is that the purpose of the negotiation process when it started 2 years ago was to prevent Iran from developing a nuclear weapon.  Even with the sanctions in place, they have been getting closer to that goal.  The agreement was designed to stop that progress.  That was the goal the partners in the negotiations agreed to try and reach.  
The purpose of preventing Iran from supporting terrorist regimes was never the purpose of the agreement.  It appears the agreement gives us as much chance to do that for at least the next decade that the first Nuclear Arms Reduction Treaty with the Russians gave us to reduce their nuclear arsenal, and ours.  There are no guarantees that Iran will not violate the agreement, which is why we have the strongest inspection terms that have ever been in place by a "rogue" nation.  

If this was such a key issue, why did we not have this discussion 2 years ago when the discussions started and the goals of the negotiations we set? It seems very dysfunctional to want to change the outcome or the purpose of the negotiations after they've been completed, based on a different set of goals. That appears to be "politics as usual", unfortunately, complaining about what has been accomplished, instead of having a rational and objective discussion of a very important issue. 

I would like to hear the opponents of the agreement discuss objectively what they believe the outcome of rejecting the agreement would be.  Have they explored this option with the allies who are part of the agreement and represent the largest component of the sanctions?  What happens if we reject the agreement on our own, but our allies don't agree to restart the process on a different basis, and to keep or strengthen the sanctions?  Might this lead to no restrictions on Iran, no inspections, and the release of billions of dollars currently frozen by the sanctions?  Isn't that a real possibility of rejecting the agreement?  The chance of needing to use military force against Iran exists in both options .... but isn't it realistic to believe that the chance of needing to use military force is less with the agreement in place, than if it is rejected? 

When people suggest that all we have to do is to reject the agreement and we can start over with a new goal, with the same sanctions in place or stronger sanctions put in place,  I don't know what facts this suggestion is based upon.  I don't hear anyone explaining what evidence they have that the rejection will be a better way to reduce the risk of Iran getting a nuclear weapon, or that it will with certainty prevent Iran from gaining relief from the sanctions put in place by other nations, who might or might not share any goal beyond preventing the development of a nuclear weapon.  No one has discussed what level of sanctions we can put in place alone, without the agreement of the other nations who have been part of the 2-year negotiation process.  

I hope readers will add their considered thinking about the issue and the options before the Congress over the next few weeks.