Former Defense Secretary Harold Brown writes in the Washington Post why he supports the deal. From the link.
Either the United States adheres to the agreement already approved by all participants (except the United States and Iran) or Congress denies U.S. adherence to the deal. If the United States and Iran join the others, Iran must dilute or export its existing enriched uranium so that it does not have enough for a nuclear weapon. The deal also would roll back, for 10 to 15 years, Iran’s capability to enrich enough uranium to be able to produce a nuclear weapon. Iran would have to convert its under-construction nuclear reactor to a form that would not fuel a plutonium-based nuclear weapon. Even if it decided to break out of the agreement this would push Iran, now probably only a few months away from having enough highly enriched uranium for a nuclear weapon, to a year away. It would take another year to produce the weapon.
http://www.msn.com/en-us/news/opinio...ner/ar-BBlIZSi