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Even undeniably "puerile" debates can sometimes cough up interesting tidbits, and, on Wednesday, Hillary Clinton proposed an interesting way to deal with Iran's nuclear ambitions: Extend nuclear deterrence to "those countries [in the region] that are willing to go under the security umbrella and forswear their own nuclear [weapons] ambitions." Unfortunately, moderator George Stephanopolous did not ask any follow-up questions, even though Sen. Clinton’s idea certainly merits a closer look.

The concept of a "nuclear umbrella" has been around almost since the Cold War and the nuclear arms race began. At the most basic level, it involves a nuclear- weapons state promising to use its nukes to respond if non-nuclear ally is attacked with nuclear weapons. Cold War strategists hoped that "extending" nuclear deterrence like this would cement important alliances and, crucially, eliminate the need for those countries to develop their own nukes. A nuclear umbrella is thus a tool of both diplomacy and of nonproliferation.

The key question here is credibility. How, for instance, would you convince the Soviets that the United States really would risk New York to defend Paris? During the Cold War, U.S. strategists achieved this credibility in several ways (pdf). First, American troops were deployed heavily in allied territory, placing them in the way of any nuclear attack. Second, U.S. nuclear weapons were often deployed in forward locations and sometimes integrated into allied command structures. Third, the umbrella only got extended to countries with which the United States already had strong alliances.

Unfortunately, even in Gulf regimes that are friendly to America, all of these preconditions are weak or nonexistent (pdf) -- which does not bode well for Sen. Clinton’s proposal. In addition, Iran does not have the ability to project power globally like the Soviet Union did, making any direct threat to U.S. interests unlikely. I should also note that any Iranian nuclear weapon is still a long ways off, and attempting to deter the Iranians is premature at this point.

However, the idea is still worth exploring as a contingency plan, and new ways of establishing credibility and commitment might be possible -- for instance, extending a missile-defense "umbrella," even one that doesn't work very well yet. But although technical measures like these may be part of the solution to U.S. problems in the Middle East, they can't supplant a broader strategy that uses all the diplomatic, political, and economic levers at America's disposal.