The North never disassociated security and political leverage with nuclear weapons elimination as did South Africa, Ukraine, Belarus, and Libya. On top of that, the Stalinist regime's persistent backsliding gave clues to the difficulty US diplomats would face in attempting to get Pyongyang to abide by its 2005 denuclearization declaration.

Now North Korea's requirement that only "mutual agreement" will permit inspection of suspect atomic sites suggests that little nuclear disarmament beyond identified nuclear sites is in the offing.

Left with this kind of legacy, the Obama administration has a hefty challenge ahead. That doesn't mean, of course, that it should stop the six-party and bilateral talks. Clearly such meetings can hold Kim's feet to the fire to honor his new responsibilities. The process may provide vital intelligence about the arsenal. Still, getting him to comply could be quixotic.

So, with the agreement in hand, Obama must pursue a new, bolder diplomatic approach in order to warm ties and cool nuclear ambitions. His administration should start with a simple step: an unconditional offer to exchange ambassadors.

In 2007, Washington and Pyongyang committed themselves to improving their relations and moving toward a full diplomatic relationship. The United States should seek to fulfill that goal next year and couple it with the formal end of the Korean War, a matter still unresolved.

Also, the opening of embassies will permit better communication and allow Washington's diplomats to better decipher the North and thus improve policymaking.

Economic ties offer a second track. Current agreements allow the North to receive economic, energy, and humanitarian assistance. Heavy oil shipments and food have followed. But Washington should do more.

Without precondition, it should throw open the doors to American investment in the North. Given the country's isolation, economic openings would expose the North Korean population to the promise of a better life. True, it may buttress the regime in the short run, but will undermine it in the long.

Military confidence-building must be a component for a more secure Korean Peninsula. Examples include establishing a hot line between Pyongyang and other capitals to deal with emerging crises, expanding military-to-military meetings, reducing the size of U.S.-South Korean military exercises, prenotifying about exercises and large military movements, and excluding of such activity near the North-South boundary.

But security also means keeping the U.S.-South Korean alliance on track by maintaining a robust conventional weapons deterrent capable of defeating the North if need be.

Then there remains one line the U.S. cannot allow Pyongyang to cross: the exporting of nuclear weapons, weapons material, or technology. Washington must tell North Korea clearly that if it contributes any nuclear item that results in a nuclear weapons incident, the U.S. will take steps to ensure the regime's prompt demise. Pursuing this hard line is key to impressing upon the North the seriousness with which the US holds the matter.

Of course, all of this will not magically eliminate North Korea's nuclear arsenal. But neither will strategies of continued nuclear negotiation, confrontation, or, given the apparent resilience of the regime, isolation.

Expanded engagement accepts the reality of the world as we find it, while offering a subtle but practical means to change it. Given time and commitment, the policy can work to undermine the political foundation that sustains the Stalinist regime, thus offering the possibility, someday, for the achievement of a truly denuclearized Korean Peninsula.

Bennett Ramberg served in the State Department during the George H.W. Bush administration. He is the author of "Nuclear Power Plans as Weapons for the Enemy."