President Obama’s North Korea policy has come to an entirely predictable dead end. Having for two years correctly resisted resuming the six party talks on the North’s nuclear-weapons program, Mr. Obama is now pressuring South Korea to do just that. This is a significant mistake. It would have been bad enough had Mr. Obama simply picked up where the Bush administration left off in January 2009, but restarting the talks now will signal weakness and indecisiveness.

Since Mr. Obama’s inauguration, Pyongyang has detonated its second nuclear device and launched two unprovoked military attacks—torpedoing a South Korean naval vessel last March and shelling Yeonpyeong Island in November, killing several civilians. Even more significant was the revelation of large, sophisticated uranium-enrichment facilities at Yongbyon, and construction there of a new nuclear reactor to replace the existing aged facility.

Resuming the six party talks, which include the two Koreas, China, Japan, Russia and America, clearly has global ramifications. Pyongyang and Tehran have cooperated closely on ballistic missiles and almost certainly on nuclear matters, as the North’s construction of a reactor in Syria, destroyed by Israel in 2007, demonstrates. It has long been a mistake to treat these rogue states as unrelated threats, a point that still eludes the Obama administration.

The talks themselves exemplify how, for almost a decade, Washington has followed Beijing’s Korea policy as if it were its own. China does not want a bellicose, nuclear North Korea destabilizing East Asia, prompting Japan and others to seek nuclear weapons. But it has definitely prized the North as a buffer state against U.S. forces in the South. China would prefer a nonnuclear North Korea but has feared to act on that goal lest the North itself collapse and the Koreas reunify. The talks are Beijing’s mechanism for maintaining the uneasy equilibrium of its contradictory policies, and keeping both the U.S. and North Korea in line.

sSouth Korean protesters hold banners during a rally against North Korea’s missiles near the U.S. Embassy in Seoul in 2009.

While South Koreans seem increasingly to be rejecting the six party approach because of the North’s aggression, Mr. Obama is working hard to squeeze President Lee Myung-bak to accept reopening the talks. Last Wednesday, before a foreign-affairs meeting, Mr. Lee said his country has “no choice but to resolve the problem of dismantling North Korea’s nuclear program diplomatically through the six party talks.” But his administration has yet to agree to a resumption of talks. Mr. Obama’s representatives are descending on Seoul, Beijing and Tokyo this week and next to torque up the pressure.

Washington should advocate America’s interests rather than China’s. Our objective should be to increase pressure on Kim Jong Il’s regime, hopefully leading to its collapse.

We should thoroughly isolate North Korea by denying it access to international financial markets, ramping up efforts to prevent trade in weapons- related materials and pressuring China to adhere to existing U.N. sanctions resolutions. Opening North Korea to foreign commerce to benefit its near-starving population, as some advocate, is utterly fanciful. If the regime had ever cared about its people, they wouldn’t be in such dire straits.

We should also dramatically expand preparations for Kim’s inevitable demise. It is a self-fulfilling prophecy for Washington to see his death only as a risk, rather than an opportunity. We should take every advantage of the inevitable rivalry and confusion that will accompany the transition, and use whatever levers are available to undermine the regime. We must also plan to meet the North’s evident humanitarian needs, whether or not there are massive refugee flows. Even if the population stayed put after a regime collapse, the North’s misery would still require urgent attention. And we must ensure that the North’s weapons of mass destruction do not fall into the wrong hands.

Many of China’s younger leaders do not reflexively support Pyongyang. Although their elders may be hopeless on the subject, the rising policy makers must hear from us that peacefully reunifying Korea is in Beijing’s long-term interests. Having a puppet state separating China from U.S. forces may once have been attractive, but forward- looking Chinese should not accept defending the North’s appalling record. This will be a hard conversation, but we have never had meaningful discussions with China on reunifying the Koreas.

While Mr. Obama is unlikely to shift his views voluntarily, Washington’s politics changed dramatically in November while Pyongyang was attacking the South and showing off its nuclear wares. After 10 years of error, we should recognize, better late than never, that unifying Korea is key to Asian peace and stability.

Mr. Bolton is a senior fellow at the American Enterprise Institute.