Imagine it is 2020. The director of the CIA requests an urgent meeting with the US president. The reason: North Korea has succeeded in making a nuclear bomb small enough to fit inside the tip of an intercontinental ballistic missile capable of reaching the continental United States. The news soon leaks to the public. High-level meetings to devise a response are held not just in Washington, but in Seoul, Tokyo, Beijing, and Moscow as well.

This scenario may seem unreal today, but it’s more political science than science fiction. North Korea just carried out its fifth (and apparently successful) test of a nuclear explosive device, doing so just days after testing several ballistic missiles. Absent a major intervention, it’s only a matter of time before North Korea increases its nuclear arsenal (now estimated at 8-12 devices) and figures out how to miniaturise its weapons for delivery by missiles of increasing range and accuracy.

It’s difficult to overstate the risks were North Korea, the world’s most militarised and closed society, to cross this threshold. A North Korea with the ability to threaten the US homeland might conclude it had little to fear from the US military, a judgement that could lead it to launch a conventional, non-nuclear attack on South Korea. Even if such a war ended in North Korea’s defeat, it would be extraordinarily costly by any measure.

That said, North Korea wouldn’t have to start a war for its nuclear and missile advances to have real impact. If South Korea or Japan ever concluded that North Korea was in a position to deter American involvement in a war on the Peninsula, they would lose confidence in US security assurances, raising the possibility that they would develop nuclear weapons of their own. Such decisions would alarm China and set the stage for a regional crisis or even conflict in a part of the world with the greatest concentration of people, wealth, and military might.

There is another risk as well. A cash-strapped North Korea might be tempted to sell nuclear arms to the highest bidder, be it a terrorist group or some country that decided that it, too, needed the ultimate weapon. By definition, nuclear proliferation increases the chances of further nuclear proliferation—and with it the actual use of nuclear weapons.

The US has options, but none is particularly attractive. As for negotiations, there’s little if any reason to be confident that North Korea would give up what it considers to be its best guarantee of survival. In fact, it has often used negotiations to buy time for further advances in its nuclear and missile capabilities.

Another option is to continue with a version of the current policy of extensive sanctions. The problem is that sanctions will not be potent enough to force North Korea to give up its nuclear and missile programs. This is partly because China, fearing large refugee inflows and a unified Korea in America’s strategic orbit should North Korea collapse, will most likely continue to ensure that it gets the fuel and food it needs.

As a result, it makes more sense to focus on diplomacy with China. The US, after consulting closely with South Korea and Japan, should meet with Chinese officials to discuss what a unified Korea would look like, so that some Chinese concerns could be met. For example, a unified country could be non-nuclear, and any US military forces that remained on the Peninsula could be fewer and farther south than they are now.

It’s of course possible or even probable that such assurances wouldn’t lead to any meaningful diminution in Chinese support for North Korea. In that case, the US would have three more options. One would be to live with a North Korea in possession of missiles that could bring nuclear bombs to US soil. The policy would become one of defence (deploying additional anti-missile systems) and deterrence, with North Korea understanding that any use or spread of nuclear weapons would lead to the end of the regime and possibly nuclear retaliation. Cyber weapons might also be employed to obstruct and impede the progress of North Korea’s program.

The second option would be a conventional military attack, targeting North Korean nuclear and missile capabilities. The danger is that such a strike mightn’t achieve all of its objectives and trigger either a conventional military attack on South Korea (where nearly 30,000 US troops are based) or even a nuclear attack from the North. Needless to say, Japan and South Korea would have to be prepared to support any US military response before it could be undertaken.

The third option would be to launch such a conventional military attack only if intelligence showed North Korea was putting its missiles on alert and readying them for imminent use. This would be a classic pre-emptive strike. The danger here is that the intelligence mightn’t be sufficiently clear—or come early enough.

All of which brings us back to that possible day in 2020. If much is unknown, what seems all but certain is that whoever wins November’s US presidential election will confront a fateful decision regarding North Korea sometime during her or his term.

Richard N. Haass, President of the Council on Foreign Relations, is the author of A World in Disarray, to be published in January 2017. This article is presented in partnership with Project Syndicate © 2016.