It is time—well past time, in my view—for the United States to cease its Cold War-style reliance on nuclear weapons as a foreign-policy tool. At the risk of appearing simplistic and provocative, I would characterize current U.S. nuclear weapons policy as immoral, illegal, militarily unnecessary, and dreadfully dangerous. The risk of an accidental or inadvertent nuclear launch is unacceptably high. Far from reducing these risks, the Bush administration has signaled that it is committed to keeping the U.S. nuclear arsenal as a mainstay of its military power—a commitment that is simultaneously eroding the international norms that have limited the spread of nuclear weapons and fissile materials for 50 years. Much of the current U.S. nuclear policy has been in place since before I was secretary of defense, and it has only grown more dangerous and diplomatically destructive in the intervening years.

Today, the United States has deployed approximately 4,500 strategic, offensive nuclear warheads. Russia has roughly 3,800. The strategic forces of Britain, France, and China are considerably smaller, with 200–400 nuclear weapons in each state’s arsenal. The new nuclear states of Pakistan and India have fewer than 100 weapons each. North Korea now claims to have developed nuclear weapons, and U.S. intelligence agencies estimate that Pyongyang has enough fissile material for 2–8 bombs.

How destructive are these weapons? The average U.S. warhead has a destructive power 20 times that of the Hiroshima bomb. Of the 8,000 active or operational U.S. warheads, 2,000 are on hair-trigger alert, ready to be launched on 15 minutes’ warning. How are these weapons to be used? The United States has never endorsed the policy of “no first use,” not during my seven years as...