The new U.S. administration assuming office next January will confront a full menu of domestic and foreign policy items demanding immediate attention.

With Hillary Clinton all but eliminated, the electorate will be choosing between the contrasting styles of Barack Obama and John McCain. The winner will be required to separate the urgent from the merely important, and will be fortunate if the Bush administration has left behind just unfinished business instead of a full-blown crisis or two.

The list of critical areas and issues is long: Iraq, the Israeli-Palestinian conflict, Afghanistan, Pakistan, Iran, and North Korea; terrorism, nuclear proliferation, human rights abuses and atrocities, global trade, climate change, pandemics, and poverty. There are also the perennial issues like managing the China-U.S. relationship as a partnership or rivalry, dealing with a prickly and newly assertive Russia, responding to requests for NATO membership from Georgia and Ukraine, and massaging the trans-Atlantic alliance.

How will the candidates respond to this agenda? The discussion can be framed with respect to four critical themes: the use of force; peace operations; nuclear weapons; and climate change. Although not exhaustive, the list is representative.

Barack Obama is the most likely to win instant international attention, admiration and respect for the U.S. His persona was formed in part in Indonesia, where he learned the triple lesson of the powerlessness and helplessness of citizens in developing countries, the status of Americans abroad, and the extent to which others look to America to help them overcome their own political and economic problems. According to him, the U.S. mission "is to provide global leadership grounded in the understanding that the world shares a common security and a common humanity." He is the most likely to engage with the rest of the world on climate change, calling on Al Gore's assistance, and by instinct should be the most responsive to providing U.S. logistical and political support for UN peace operations in Africa. He is also the only one to have shown interest in pursuing the goal of a nuclear-weapons-free world and ratifying the Comprehensive Test Ban Treaty.

He is circumspect on the use of force, for example against Iran. He has shown the clearest understanding of the broader damage done to U.S. interests and leadership by the distraction in Iraq and promised to bring it to "a responsible end." Yet he also famously said that he would not hesitate to take military action inside Pakistan even without the host government's permission if there was actionable intelligence to indicate the presence of high value terrorist leaders there. Overall, nonetheless, he is likely to strive to "harness American power to reinvigorate American diplomacy."

John McCain knows first-hand what war means. The misrepresentations of his 100-years-in-Iraq comment notwithstanding, he has based his campaign on winning the war in Iraq and not losing focus from the war on terrorism. He seems more interested in co-operating with a coalition or league of democracies than giving priority to the United Nations.

Based on that, like George W. Bush, he would most likely differentiate between U.S.-friendly and U.S.-hostile regimes possessing or pursuing nuclear weapons, enlisting the former as strategic partners and allies while sanctioning the latter as threats to world peace. But he could also offer Reaganesque surprises if the idea of a nuclear-weapon-free world propounded by four former Republican heavyweights grabs his attention.

Neither by personal instinct nor by party leanings is Mr. McCain likely to pursue an activist agenda with respect to UN peace operations and climate change. Moreover, as he is less likely to serve for a second term (based simply on age), he may have less long-term impact.

Regardless of who becomes president, to regain its former status as a good international citizen, the U.S. should reinvest diplomatic assets in the United Nations, regain its former role as the champion-in-chief of the global human rights norm, "re-sign" and ratify the Rome Statute of the ICC that was "unsigned" by Mr. Bush in 2002, reaffirm firm adherence to the Geneva and UN torture conventions, ratify the CTBT, and assume the leadership role in negotiating a post-Kyoto climate deal.

Finally, what of the relationship with the United Nations? In Afghanistan, the two are already working together closely and have done so from the start. This is one reason why the U.S. role in Afghanistan remains relatively uncontroversial. In Iraq, for U.S. troops simply to withdraw would create a dangerous vacuum. Only the UN has the legitimacy to authorize a replacement multinational presence for stabilizing the security situation and the capacity to mobilize the requisite resources for post-conflict reconstruction in Iraq. Regarding Iran, any military attack without UN authorization would reopen America's Iraq wounds around the world with a vengeance.

Though the hyperpuissance may be humbled, the U.S. is neither a humble nor a dispensable power. Nor is the UN a disposable organization, even for the most powerful nation in history. It remains an unsubstitutable forum and an indispensable font of authority for reducing the transaction costs of U.S. diplomatic engagement with the rest of the world.

Within the urgent and important issues, the new administration will therefore have to pay early attention to repairing and revitalizing the relationship with the United Nations that has been strained and frayed.

The opinions expressed in this article/multimedia are those of the author(s) and do not necessarily reflect the views of CIGI or its Board of Directors.