Obama's deal on weapons could win Russia's cooperation on tougher issues later.

It's odd that in the "post-Cold War era," with all the common interests and urgent problems that the United States and Russia could discuss, the issue on which the two presidents lavished the greatest attention and achieved the most substantive progress at their summit in Moscow this week was the hoariest track from the Cold War playbook—strategic nuclear arms talks.

Then again, while it's odd, it's not so surprising.

Even during their heyday, in the 1970s and '80s, the chief benefit of SALT, START, INF, and the assorted other nuclear negotiations wasn't so much their specific outcomes as that they gave the superpowers something to talk about—a forum in which their diplomats could engage one another, exchange information, probe and sometimes expand the limits of cooperation—in an era when it was impossible to talk fruitfully about anything else.

To some degree, after the gloom-ridden years of George W. Bush (which exacerbated Vladimir Putin's nationalistic paranoia), we're in that spot again. If there really is a "reset button" in U.S.-Russian relations, nuclear arms talks provide a familiar vocabulary—and, even more, a very high chance of success—to get the process under way.

It would have been a grave mistake if President Barack Obama had come to Moscow with an agenda that focused solely on strategic arms talks. One lesson learned from the bad old days: If nukes are all the two powers can talk about, relations very quickly devolve into fetishism.

Back then, at the height of the Cold War, many diplomats, politicians, think-tank denizens, and journalists immersed themselves so thoroughly in the esoterica of "nuclear-exchange" calculations, missile throw-weight ratios, and "hard target kill" probabilities that they came to confuse this bizarre, abstract world for the real one.

Dip into the archives of such journals as Foreign Policy, Foreign Affairs, International Security, even the op-ed pages of major newspapers from that era, and you will find serious-minded officials and scholars spinning elaborate, quantitative (and, therefore, presumptively scientific) scenarios in which the Soviet premier launches a nuclear attack against the United States—hurling thousands of nuclear warheads, which explode with the force of billions of tons of dynamite (thousands of megatons) and spread vast plumes of radioactive fallout, killing tens of millions of Americans—because the calculations suggest that his most potent nuclear warheads could destroy all our land-based intercontinental ballistic missiles in a surprise first strike.

Such scenarios ignored a few basic facts: that U.S. submarines, prowling under the ocean's surface and thus invulnerable to attack, would still hold thousands of nuclear warheads, which could be fired against the USSR in a devastating retaliatory blow; that some of the land-based missiles and bombers would survive the first strike as well; and that—above all else—the whole mathematical exercise simply did not reflect the way that any leader of an established power, including Russia, has ever thought about the use of force.

Certain calculations suggested that during the early 1980s, the Soviets did possess this theoretical "first-strike capability"—then-Defense Secretary Caspar Weinberger warned of a "window of vulnerability." Yet there is no evidence whatsoever—in the since-declassified Russian archives or anyplace else—that this "edge" altered the balance of power or emboldened the Soviets to take steps or issue threats that they otherwise might not have.

One can go further. In the late 1960s, Soviet and Chinese armies confronted each other, and nearly went to war, over a territorial dispute along the Yulu River. Yet the Kremlin leaders backed off because Mao Zedong possessed a mere handful of nuclear weapons and they feared that he might launch them in response to an invasion.