During that first debate, Kerry vigorously criticized the Bush record on the proliferation of nuclear weapons and materials necessary to their creation. Bush's replies suggested that, though he sees the danger of a 9/11 attack gone nuclear, he didn't seem to understand that policies of his own administration were making that nightmare prospect more likely, not less. Indeed, regarding the nuclear threat, the Bush administration has become an inadvertent partner to America's sworn enemies.

Kerry would reverse this movement, and he said how. Kerry singled out three crucial Bush mistakes:

• Unsecured nuclear material in the former Soviet Union remains the gravest terrorist danger. For all Bush's talk about 9/11, he has done less to meet this danger in the two years after the World Trade Center attacks than was done in a comparable period before. In the debate, Bush bragged of a "35 percent increase" in funding to secure loose nukes, but the number is hollow. At present rates the problem will be addressed in 13 years. Kerry promised to do it in four.

• Bush is failing to stop nonnuclear nations from going nuclear. North Korea makes the point. In the debate, the president rejected bilateral negotiations in favor of six-party talks that had, in effect, already collapsed. Iran, too, has found in Bush only reasons to pursue nukes. Iran's rejection of inspections by the International Atomic Energy Agency was reinforced this month when Brazil blocked agency oversight, with little protest from Washington. In fact, Brazil embodies Bush's failure -- a nation that repudiated its nuclear weapons program in 1990 once again at the mercy of its own nuclear hawks. Bush policies encourage foes and friends alike to pursue nukes -- or to seek leverage by threatening to.

• Bush keeps the nuclear future alive by devoting hundreds of millions of dollars -- and precious political capital -- to develop a new generation of nukes, so-called earth-penetrating nuclear weapons. As Kerry put it, "You talk about mixed messages. We're telling people, `You can't have nuclear weapons,' but we're pursuing a new nuclear weapon that we might even contemplate using." Referring to himself, Kerry then said, "Not this president. I'm going to shut that program down."

One of the great achievements of the Cold War was the creation of an antiproliferation international order, embodied in the Nuclear Non-Proliferation Treaty, first agreed to in 1968, and renewed in 1995. It is a triumph of diplomacy and political hope that, almost 60 years after the Trinity atomic bomb test, there are so few nuclear powers. But the main reason non-nuclear states agreed to foreswear the development of these weapons was the commitment made by the nuclear states, embodied in Clause VI of the treaty, to move toward the eventual elimination of nuclear weapons.

The Bush administration's devotion to a new round of nuclear development breaks that commitment, and inevitably weakens the antiproliferation order. That is the dread implication in Brazil's unexpected defiance of the International Atomic Energy Agency. A new age of proliferation is just beginning, and George W. Bush is its father.

Kerry is on record in this campaign as wanting to move in exactly the opposite direction. Across two decades in the US Senate, especially as a main supporter of the Nunn-Lugar Cooperative Threat Reduction Program, Kerry has shown that he understands the urgency of turning the worst legacy of the Cold War back on itself.

In his challenges to President Bush's unilateralism, Kerry has demonstrated his commitment to working with other nations as the only way to make the world safe from nuclear terrorism -- a commitment Bush mocks as a "global test." Across the range of issues, from nuclear diplomacy to threat reduction to the trap of earth-penetrating nuclear weapons, Kerry has shown his mastery of the political and military complexities, just as, in response, Bush has put on display his cynical ignorance. In other matters, the president's ineptness and two-facedness are disheartening, but here they represent a mortal danger.

On this one issue alone -- keeping nuclear weapons away from terrorists -- the election should turn. John Kerry for president.

James Carroll's most recent book is "Crusade: Chronicles of an Unjust War." 

© 2004 Boston Globe