This is the standard I use to measure the Agreement:
Does it better protect the United States and Israel than any available alternative?
This requires examination of both the Agreement and the available alternatives.
The two alternatives most often suggested are continuation of the existing sanctions and massive, sustained conventional air attack. At this time, neither will serve us as well as the proposed Agreement.
The Agreement puts upwards of 130 pairs of boots on the ground. Annex I, pp. 68 on p. 39. Neither the existing sanctions regime nor a massive conventional air attack nor any other available alternative does this. While imperfect, there is simply no good substitute for embedded, trained nuclear weapons investigators experienced in ferreting out deceptive processes, procedures and facilities.
Sanctions have reached their limit. The United States can unilaterally cut Iran off from the U.S. economy and international banking. We cannot unilaterally cut off oil sales to China. If it chooses to, China can absorb all the oil Iran can produce. China has signed off on the Agreement. Essentially China says Iran's compliance with this Agreement is sufficient for China to resume unrestricted purchase of Iranian oil. The European Union says Iran's compliance with the Agreement is sufficient to resume doing business with Iran. With that Iran can survive well enough. We no longer have an effective sanctions regime.
Over time the United States has the ability to sufficiently degrade Iran's air defenses to permit extended attacks on nuclear production facilities Iran has deeply buried under its mountains. That is, we can attack the facilities we are able to remotely track. However the rest of the world has determined that Iran's compliance with this Agreement would be sufficient. Repudiation of the Agreement and massive attack will leave the U.S. an outcast - we would inherit Iran's pariah status.
At every stage of the Agreement Iran is prohibited from obtaining nuclear weapons - 8 years, 10 years, 15 years, 25 years. At any point that Iran moves to violate that prohibition, the moral weight of the world swings to our favor and we will be in position to re-impose sanctions or take such other actions as we may deem appropriate. The advantage to us is, after however many years of boots on the ground, we can have a much better idea where to focus such action.
For these reasons I support the proposed Iran nuclear Agreement. Plainly put, the next time I am in Israel, I will feel safer with this Agreement than without it.