The Obama administration labored strenuously to produce a fourth round of sanctions against Iran in the UN Security Council. The broader question is whether more sanctions are likely to persuade Iran to give up its pursuit of an indigenous nuclear capability—or even to get the regime to stop enriching uranium.

I know of no expert or government official who believes that will happen. It is always possible that this pessimism is wrong. Miracles occasionally happen. But the sanctions approach is unlikely to solve the problem.

Neither is the diplomatic offer brokered by Brazil and Turkey but rejected by Washington. Still, given the limited dividends promised by sanctions, Washington should have considered foregoing the sanctions in favor of the deal. The impact of the agreement, like the impact of the sanctions, would be limited, but it would have removed more than half of Iran’s existing fissile material and held a small possibility of a diplomatic resolution of the problem.

Instead, we are left waiting to see whether the new sanctions will cause a fundamental shift in Iran’s behavior.