The BBC reports Hillary Clinton's answer to a question about a hypothetical nuclear attack by Iran on Israel:
As the candidates appeared on the US talk show circuit on Tuesday morning, a row erupted when Mrs Clinton was asked how she would respond if Iran launched a nuclear attack on Israel.
She replied that: "If I'm the president, we will attack Iran... we would be able to totally obliterate them.
"That's a terrible thing to say, but those people who run Iran need to understand that, because that perhaps will deter them from doing something that would be reckless, foolish and tragic," she told TV channel ABC.
In response, Mr Obama said: "Using words like 'obliterate' - it doesn't actually produce good results, and so I'm not interested in sabre-rattling." He said only that Iran should know he would respond "forcefully" to an attack on any US ally.
It does of course sound a terrible thing to say. But Senator Clinton is right and Obama wrong. For nuclear deterrence to hold, it is essential that Iran - a regime that is autocratic but aware of costs - understand the consequences of nuclear brinkmanship. To say Iran would meet a "forceful" response in the event of a nuclear strike is a feeble comment that would not effectively deter. The only response to a nuclear strike that could prevent military victory by an aggressor is a countervailing nuclear strike. Leaving open the possibility, even implicitly, of a purely conventional or even a diplomatic response is to soften deterrence.
We have been here before. The closest the world has yet come to a nuclear exchange was the Cuba missile crisis in 1962. Several factors combined to resolve that standoff. We now know that the Kennedy administration reached a covert understanding whereby the US would withdraw Jupiter and Thor missiles from Turkey. But it was also crucial, early in the crisis, that Kennedy made clear the consequences of a nuclear strike from Cuban soil on any US ally. "It shall be," declared JFK, "the policy of this nation to regard any nuclear missile launched from Cuba against any nation in the Western Hemisphere as an attack by the Soviet Union on the United States, requiring a full retaliatory response upon the Soviet Union."
Khrushchev was an impetuous leader but not a suicidal one. He understood in his gut the potential cost of persisting with missile deployment. (He was also scared witless by the urging of Castro to launch a nuclear first strike on the American mainland in the event of an invasion of Cuba.) Whatever else you might say about the candidature of Senator Clinton, it is to her credit that she understands that precedent. Iran must know exactly what would happen in the event of a nuclear strike on Israel or any other American ally. This would apply both to an attack by Iran directly and to an attack by a proxy terrorist group armed with a rudimentary "dirty bomb".