Iran simply cannot be allowed to achieve nuclear weapons capability. I have no idea how close they are to that goal. So what is the solution?
There are many possible solutions. All of them are bad. Many of them involve nuclear detonations in multiple places.
One might reasonably assume that Iran has a few atomic weapons right now. They have had plenty of time to acquire the necessary materials, and the technology for simple devices has been readily available since the 1950's. Iran has good engineers. They can make atomic weapons. What Iran does not have is an effective delivery system.
What Iran is also missing is a reliable command-and-control system. Their government is composed of factions with bitter rivalries between them and no faction can really trust other factions with control of nuclear weapons. Most likely, their equivalent of "permissive action links" are held by different members of hostile factions.
Another aspect is that the Russians cannot be terribly comfortable with a nuclear-armed Iran. It is within possible bounds of consideration for the Russians to provide Israelis with targeting information or other vulnerabilities so that the Israelis can destroy all weapons and facilities used to make them. The Iranians have probably considered this as well.