Mark Dubowitz and Reuel Marc Gerecht, writing in the Wall Street Journal:
Iran's oil exports have been halved by economic sanctions, but that still leaves the regime with around $50 billion in oil income this year, according to calculations by the Foundation for Defense of Democracies. Nevertheless, the Iranian economy has taken a substantial hit from sanctions. After the rial lost nearly half of its value in a week earlier this month, Tehran began severely restricting access to dollars and euros.
That's a welcome sign for anyone who hopes that international sanctions will cause the Tehran regime to abandon its nuclear-weapons program. But the currency restrictions were also a warning: In all probability the regime is battening down the hatches, husbanding foreign-exchange reserves, and preparing for a long ordeal. Given the progress that Tehran has already made with its nuclear plans—still-hidden centrifuge manufacturing plants, enrichment facilities at Natanz and Fordow, a likely weaponization facility at Parchin, and an extensive ballistic-missile program—the regime faces a short, relatively inexpensive dash to the nuclear finish line.
How close it is to that finish line, and how much more time should be allowed for sanctions to work before it's too late, and a pre-emptive military strike becomes essential?
The first task in answering the question is to make a solid guess about the Islamic Republic's economic cripple date. That will arrive when its hard-currency reserves are insufficient to cover its hard-currency payments; when the import of foreign goods is no longer possible; when the rial becomes worthless paper; and when precious metals and barter become the only means of exchange.
Whole thing here.