You Keep Using That Word 'Deterrence'...
It doesn't mean what you think it means.
Dennis Ross thinks threatening Iran more will somehow discourage them from building a nuclear deterrent:
To improve U.S. deterrence in the long run, Washington should publicly declare what Tehran will lose if it continues down its current path—and what it will gain from changing course. The aim must be to restore Iran’s fear of U.S. military action without putting the country in a corner with no diplomatic way out.
There are few words that are misused and misunderstood more often than deterrence, and Ross’ article is a good example of how this can lead to terrible policy recommendations. The problem here is twofold: the Iranian government likely has much greater difficulty believing promises of sanctions relief than it does threats of attack, and threats of attack give their government an added incentive to accelerate and escalate their program. The more afraid of U.S. military action the Iranian government is, the greater its incentive will be to develop its own deterrent to ward off a future attack.