Current U.S. policy toward the regime in Tehran will almost certainly result in an Iran with nuclear weapons. The seemingly clever combination of the use of "sticks" and "carrots," including the frequent official hints of an American military option "remaining on the table," simply intensifies Iran's desire to have its own nuclear arsenal. Alas, such a heavy-handed "sticks" and "carrots" policy may work with donkeys but not with serious countries. The United States would have a better chance of success if the White House abandoned its threats of military action and its calls for regime change.
Consider countries that could have quickly become nuclear weapon states had they been treated similarly. Brazil, Argentina and South Africa had nuclear weapons programs but gave them up, each for different reasons. Had the United States threatened to change their regimes if they would not, probably none would have complied. But when "sticks" and "carrots" failed to prevent India and Pakistan from acquiring nuclear weapons, the United States rapidly accommodated both, preferring good relations with them to hostile ones. What does this suggest to leaders in Iran?
To look at the issue another way, imagine if China, a signatory to the nuclear Non-Proliferation Treaty and a country that has deliberately not engaged in a nuclear arms race with Russia or the United States, threatened to change the American regime if it did not begin a steady destruction of its nuclear arsenal. The threat would have an arguable legal basis, because all treaty signatories promised long ago to reduce their arsenals, eventually to zero. The American reaction, of course, would be explosive public opposition to such a demand. U.S. leaders might even mimic the fantasy rhetoric of Iranian President Mahmoud Ahmadinejad regarding the use of nuclear weapons.