What makes nuclear deterrence work? That was the great strategic debate of the 20th century, as argued between two towering intellects from RAND. In one corner loomed Herman Kahn. The rotund, flamboyant defense analyst insisted defensive capabilities were essential to establishing an effective deterrent. If you could fight and survive a nuclear conflict, your enemy would think twice before pushing the button.

In the other corner, rail-thin Tom Schelling argued that stability came from a balance of terror. Defenses were not only unnecessary, they were undesirable; real security came from the fear that when the "balloon went up," everybody died.

Schelling won. Both Democrats and Republicans accepted his strategy as a matter of faith. Mutually Assured Destruction (MAD) became the cornerstone of U.S. defense doctrine. The only acceptable means to mitigate MAD were arms control pacts -- treaties in which both sides agreed to synchronized reductions in their nuclear firepower.

This is all history that matters. When President Obama rattles off a list of old-guard Republicans supporting the New START nuclear arms reduction treaty with Russia, he presents it as evidence of bipartisan backing.

But he's really just rattling off a roster of "old think" relics of the Cold War era who still believe that the strategy they followed in the bygone world of two nuclear super powers still makes sense for the 21st century. The fact that they're Republicans is immaterial. The fact that their views are outdated and dangerous is not.

In today's world, Kahn's strategy of "protecting and defending" against nuclear threats makes far more sense. Today, instead of two atomic gunslingers facing-off in the street, there is a global gaggle of nuclear and near-nuclear states spread out all over town. They don't all play by the same rules.

If someone gets an itchy trigger finger, it is much more likely to result in a melee than a standoff. In an era in which nuclear weapons technology is spreading rapidly -- and into increasingly unpredictable hands -- nuclear relationships are too unstable to depend on MAD.

Of course, Moscow still loves MAD. That's why they signed the New START nuclear agreement and why the Duma now insists the treaty limits missile defense. They want the U.S. to remain vulnerable to Russia's nuclear threat.

In this way, Russia can stand as America's military equal, despite its far inferior military power. New START gives Moscow parity on the cheap. The White House was mad to let Moscow gets its way.

In an unstable world marked by expanding proliferation of nuclear weapons, missile defense is much more attractive (indeed, necessary) than when Kahn first made his case. Comprehensive missile defenses create grave doubts among our enemies that their weapons can get through. They also give the defenders options other than just threatening nuclear holocaust for responding to threats from other atomic states.

Combined with strong conventional forces, and aggressive counterproliferation operations to dampen lesser threats and deal with the challenge of nuclear terrorism, a "protect and defend" strategy offers great advantages.

First, it provides a real, concrete defense against nuclear attack. Second, it allows us to negotiate meaningful arms control agreements from a position of strength.

Obama is no nuclear strategist. Upon entering the Oval Office he simply adopted conventional "old think." Sure, he gets lots of cheerleading from the left and accolades from last century's leaders. The former lives in the world it wants, the latter in the world that used to be.

But MAD is the wrong strategy for the 21st century, and no amount of back-slapping from former officials can compensate for that grave error.

Examiner Columnist James Jay Carafano is a senior research fellow for national security at the Heritage Foundation.