Not very. As Dan Drezner points out, the sanctions serve to divide the Iranian leadership, but paradoxically, divisions among the members of the leadership class only serve to diminish Iran’s incentive to negotiate with the West over its nuclear program. In the meantime, the Iranian people suffer, since the costs of the sanctions are passed down to them.
As Professor Drezner’s post also notes, the sanctions appear to be pushing the United States to an unofficial policy designed to bring about regime change in Iran. I am all for regime change in Iran (though I don’t want to go to war in order to do it), but if regime change is going to be an option, then it is one that the United States ought to actively embrace in order to make the option work. Regime change won’t work if it is just a default option for the United States; one that the U.S. is forced to adopt for lack of better options, and one that the U.S. adopts unenthusiastically.
All of this, of course, ought to be remembered the next time the Obama Administration–or any of its partisans–boast about how effectively the sanctions against Iran are working. But since it is an election year, basic truths about the sanctions on Iran will be forgotten.