John McCain and Barack Obama are two of the most remarkable Americans to enter public life. Both men are extraordinarily capable and their campaigns — which began against great odds — reflect that. And yet with respect to national security, neither campaign has articulated the fundamental points of view that will allow people to make an informed choice in November.

Time is running out. Without understanding how these two leaders approach and analyze problems, without having a clear sense of their differentiated approaches, we will be mired in the ephemera of polls, horse race journalism and the petty exchange of complaints arising from alleged missteps.

Here, then, just after the anniversary of 9/11, a day when both candidates chose to put politics aside and appear together at ground zero, are a dozen questions we would like to see them address. We know both candidates differ on Iraq and agree on closing the Guantanamo prison camp. We also know that both are for change, that they are patriotic and that they are cautious. But we hope they will not be too cautious to give us clear answers, even when these might alienate some voters.

PAKISTAN

Afghan officials have charged that some elements of the Pakistani government are seeking to undermine their country by giving sanctuary to Taliban and al-Qaida groups that cross the border to attack Afghanistan. Would you launch large-scale armed attacks against terrorists in Pakistan if the new government there is unwilling — or unable — to suppress these groups and refuses to give United States forces permission to act? Or are you willing to put the Afghan regime at risk to play for time in Pakistan, hoping that a more successful government will emerge in Islamabad, and fearing that any attempt to use force there will result in a nuclear-armed anti-Western state?

DARFUR

For some years, the world has watched while ethnic cleansing — even genocide — has gripped Darfur. Are you prepared to announce the rules for American intervention for humanitarian purposes and, if so, what would those rules be? Would you be willing to organize a coalition of states to intervene? Or should the United States defer to the United Nations or regional organizations — even when they are deadlocked and unable to act?

IRAQ

It has been more than five years since the United States-led coalition removed Saddam Hussein from power. How long should American troops remain in Iraq if American commanders on the ground state that withdrawal would lead to chaos? That is, should the United States withdraw according to a predetermined timetable, even if the consequences appear dire for Iraq? Or should troops remain indefinitely until their withdrawal can be assured to leave behind a stable Iraq?

IRAN

Would you authorize the use of force by the United States — or collaborate with Israel — to prevent Iran from developing nuclear weapons if it appears that diplomatic efforts are failing to bring about substantial progress in this regard? If not, what further incentives would you offer Iran to end its nuclear programs? For example, would you be willing to press Israel to do away with its own nuclear weapons as part of a regionwide denuclearization? What incentives would you be prepared to offer Israel to desist from a pre-emptive attack? Would you be willing, for instance, to give Israel a place under the United States nuclear umbrella?

PRISONERS' RIGHTS

The Supreme Court recently held that prisoners taken in the war against terror are entitled to habeas corpus review in the federal courts. Is it sensible to speak of a "war" on terror, or is this a struggle that should be principally handled by law enforcement? Should suspected terrorists be given the same protections as ordinary criminals — like the right to confront their accusers and the right not to be tried by illegally obtained evidence? Or should there be special rules for the trials of terror suspects, or even a special court that would hold secret trials?

NATO

In light of U.N. Security Council inaction in Bosnia, Cambodia, Rwanda, Zimbabwe and elsewhere, critics have said that the United Nations is not an effective instrument for confronting rogue states, terror and genocide. Do you favor expanding NATO, or using it as a model for creating an alliance of democracies? If you do, would such an alliance require unanimity of its members for action? Or, if you oppose creating such a group, how should the United States confront crises when the council is paralyzed?

TRADE AGREEMENTS

What, if anything, should the United States do to further trade negotiations after the collapse of the Doha round in Geneva? Should the United States try to revive multilateral talks, and, if so, how? Do you support bilateral trade agreements with Colombia, South Korea and Panama? Should the United States abrogate NAFTA if Canada and Mexico will not revise the agreement to our liking?

RUSSIA

Russia's invasion of Georgia followed Georgia's attack on the separatist region of South Ossetia; it also was an expression of Russian resentment over former Warsaw Pact states becoming members of NATO and hosting proposed American missile defense systems. Would you try to restore Georgian sovereignty over South Ossetia and Abkhazia? If so, how — by offering U.S. security guarantees to Georgia, expelling Russia from the Group of Eight, withholding membership in the World Trade Organization? Or would you attempt to calm Russian sensibilities by renouncing, at least for the time being, Georgian and Ukrainian candidacies for NATO membership, and putting Polish and Czech missile defense deployments on hold?

GLOBAL PARTNERSHIPS

Both of you have talked about global partnerships to address problems as varied as climate change, weapons proliferation and terror. What specific incentives can you offer potential allies to create such partnerships? Why do you believe these incentives will be more likely to succeed than those offered by the Bush and Clinton administrations?

ENERGY

Political instability in the Middle East underscores the need for Western energy security. At the same time, the Group of Eight has set a goal of bringing global carbon dioxide emissions down to half their 1990 level by 2050. Realistically, there is little chance of achieving this target, nor of achieving real energy security, without drastically new technologies. What, if anything, should government do to increase domestic production of oil and gas, to expand the use of nuclear energy and to encourage energy conservation and new technologies? Which technologies do you favor and how should government promote them — or with high oil prices, would you leave this job to the market?

FOREIGN AID

Rising food prices and population growth raise the specter of widespread starvation in Africa. The overseas aid budgets of most countries, including the United States, are far below the United Nations Millennium Development Goals' target of 0.7 percent of gross domestic product. Would you favor greatly increasing this aid to meet those levels or would you, instead, try to wean Africa off direct aid in favor of using these funds to spur investment in the region?

NATIONAL SECURITY

What do you see as the principal difference between you and your opponent in your fundamental approach to the national security problems facing the United States?

Choice is at the heart of the American electoral idea. If Americans are given a clear choice — as they were in 1964 and 1980 — they can speak with clarity at the ballot box. If not, the winning candidate will risk inheriting a fragile mandate that will soon erode in the face of the challenges he avoided forthrightly addressing in the campaign. As 9/11 painfully reminds us, these challenges insistently reassert themselves.

Philip Bobbitt, the author of "Terror and Consent: The Wars for the 21st Century," is a law professor at Columbia and a fellow at the University of Texas. John C. Danforth, a former Republican senator from Missouri, was the United States ambassador to the United Nations from 2004 to 2005. They wrote this commentary for The New York Times.