During the first presidential debate in 2004, President Bush and Sen. John Kerry agreed -- as stated by the president -- that "the single, largest threat to American national security today is nuclear weapons in the hands of a terrorist network." Yet despite that consensus, the subject of weapons of mass destruction proliferation has quickly disappeared from the national agenda.

Few comments or questions on this issue have been posed to the presidential candidates, even though preventing WMD proliferation should be on the short list of priorities for a McCain or Obama White House. And it rarely appears on polls of the most urgent concerns of citizens. So, in 2008, after seven years in which there have been no successful terrorist attacks inside the country, why not relax? Here are the reasons:

Terrorists have continued to demonstrate the intent to acquire a WMD capability. As Director of National Intelligence Admiral Michael McConnell said in his Sept. 10, 2007, testimony to the Senate Homeland Security and Governmental Affairs Committee, "al Qaeda will continue to try to acquire and employ chemical, biological, radiological, or nuclear material in attacks and would not hesitate to use them if it develops what it deems is sufficient capability."

The potential human toll of an attack utilizing weapons of mass destruction is appalling. On a normal workday, half a million people crowd the area within a half-mile radius of Times Square. A noon detonation of a nuclear device in Midtown Manhattan would kill them all.

Another attack -- particularly with WMD -- would have a devastating impact on the American and the world economies. As former U.N. Secretary General Kofi Annan warned, a nuclear terrorist attack would push "tens of millions of people into dire poverty," creating "a second death toll throughout the developing world."

The environment for the use of nuclear and biological weapons has changed. Although Russia is doing a better job of securing its stockpiles and therefore is less of a threat, North Korea and Iran have taken its place. North Korea has gone from two bombs worth of plutonium to an estimated ten. Iran has gone from zero centrifuges spinning to more than 3,000.

In what some have termed a "nuclear renaissance," many nations are now seeking commercial nuclear power capacity that will add to the inventory of nations and scientists who could extend their interest to nuclear weapons.

With the nuclear surprises we've experienced in Iran, Syria and North Korea, it is clear that current nonproliferation regimes and mechanisms can no longer be certain to prevent more nuclear proliferation or the theft of bomb-usable materials.

Biologists are creating synthetic DNA chains of diseases which have been considered extinct, such as the 1918 influenza virus that killed over 40 million people. The potential of using these laboratory-developed strains against an unaware and noninoculated population is ominous.

There is the necessity of engaging the American people. Unlike the Cold War, which was a superpower vs. superpower confrontation, the current asymmetric threat that would be dramatically escalated if the terrorists had access to nuclear or biological weapons. The incorrect claims regarding Saddam Hussein's WMD and his collusion with al Qaeda have contributed to public skepticism. Nonetheless, there was and is a real danger that al Qaeda will get a nuclear bomb and attack an American city.

Faced with the possibility of a mushroom cloud over Manhattan, many people are paralyzed by a combination of denial and fatalism. The president is the best position to rally the resilience and patriotism of Americans to this threat.

We have been asked by Congress to lead a bipartisan commission to assess the current state of our nation's policies to prevent the proliferation of weapons of mass destruction into the hands of rogue states and nonstate terrorists. Our final report will be released in November. Based on our assessment, we will make recommendations to the new Congress and the new president.

We trust that the president and Congress will recognize the primacy of this threat and the consequences should it come to pass. Nuclear terrorism has been described as the ultimate avoidable catastrophe. Whether it -- and other WMD catastrophes -- will be avoided will depend in large part on where it ranks among the 44th president's priorities.

Bob Graham, a former U.S. senator from Florida, is chairman of the congressionally established Commission on the Prevention of WMD Proliferation and Terrorism and the board of oversight of the Graham Center for Public Service at the University of Florida and the University of Miami. Jim Talent a former U.S. senator from Missouri, is vice chairman of the WMD Commission and Distinguished Fellow at the Heritage Foundation.