Sometime over the next several years, the next U.S. president could confront a genuinely dangerous threat from a faraway place -- a North Korean missile that can hit U.S. territory with a nuclear warhead.

Led by an impulsive and brutal young man, North Korea may pose the most direct nuclear risk to the United States. Kim Jon-un is a weak leader in every respect but one -- he pushes ahead relentlessly on a program to build missiles that can reach Guam and other American targets carrying miniaturized nuclear warheads.

A nuclear North Korea, remote as it may seem, poses what Pentagon planners see as an urgent challenge for the United States. Officials say the situation requires close monitoring and contingency plans for how to respond to a range of scenarios in which a reckless or imploding Pyongyang might actually attack.

The Obama administration’s strategy has been to work with China to contain Kim and seek a de-nuclearized North Korea. The U.S. lauded China’s decision to support a U.N. Security Council resolution in March that condemned North Korea’s nuclear and missile tests and imposed limited sanctions. China and the U.S. are working “cooperatively,” notes a South Korean official, but he cautions that they are moving at a different “intensity and speed.”

China wants to go slow on North Korea, as with most foreign policy issues. But U.S. planners wonder if they can afford that leisurely pace in dealing with a country that warned just three months ago that it might launch a “pre-emptive and offensive nuclear strike” against a joint U.S.-South-Korean military exercise.

“China needs to understand that this is not working,” argues Kurt Campbell, a former assistant secretary of state for Asia and a key adviser to presumptive Democratic presidential nominee Hillary Clinton. “China continues to take small steps,” he says, but what’s needed are much tougher sanctions of the kind that brought policy change in Iran and Myanmar. If China won’t join in such punishing sanctions, he says, the U.S. may have to impose them unilaterally.

Japan and South Korea, which are already targeted by North Korean missiles, share the U.S. concern. Japanese analysts see some signs that China has been tightening its border with North Korea, in a demonstration of compliance with the U.N. resolution. South Korean analysts agree that China has taken some positive steps, but they note that China is still a big importer of North Korean coal.

Despite the growing international concern, North Korea keeps pushing ahead. Ignoring the March passage of the U.N. resolution, Pyongyang conducted three subsequent tests of its “Musudan” intermediate-range missile. U.S. analysts believe the Musudan is designed to target American territory in Guam, near-term, while the North Koreans develop bigger, intercontinental ballistic missiles that could strike Hawaii, Alaska or the U.S. mainland.

North Korean media have also shown Kim examining nose cones that could carry a nuclear warhead. South Korean analysts say that in every recent nuclear test, the North Koreans have focused on making a smaller, lighter weapon that could fit atop a missile.

The U.N. sanctions regime seems to have had no effect in curbing these provocative actions. The Security Council last week condemned the three recent missile tests as a “grave” and “flagrant” violation of its March resolution and called for countries to “strengthen enforcement.” But the U.N. left open the question of how to get tougher.

North Korea is the biggest headache in an Asian security situation that, overall, may top the agenda for the next president. The other flashpoint is the South China Sea, where the Obama administration recently has been signaling new resolve against Chinese sovereignty claims.

Defense Secretary Ashton Carter warned in Singapore last weekend that Chinese attempts to reclaim land on the disputed Scarborough Shoal would be “provocative and destabilizing” and would trigger unspecified U.S. “actions” in response. And Secretary of State John Kerry, during a recent visit to Mongolia, made a similar warning against any Chinese attempt to impose an “air defense identification zone” in the South China Sea.

China’s response? Some Asian analysts think Beijing has gotten the message and slowed the pace of its expansion in the South China Sea, for now. But this week, Chinese jets buzzed a U.S. RC-135 reconnaissance plane in the contested area, at what U.S. officials said was an “unsafe” speed.

The Middle East and Europe are on any new president’s agenda. But next January, it may be North Korea and the surrounding Asian theater that deserve the most urgent look from the new commander in chief.

David Ignatius’ email address is davidignatius@washpost.com. -- Ed. 

(Washington Post Writers Group)