I've never heard of the South Korean island Yeonpyeong before. My guess is that you haven't, either. And that, until yesterday, President Obama, too, was clueless about it.

No longer. The North Koreans have been using it as target practice, killing two South Korean soldiers on the small military installation and shelling the homes of dozens of civilians. The North is once more about to show that it can undertake pinprick attacks with impunity against the South, taunting both it and its American protector with their helplessness. Ditto for showing off their "secret" nuclear plant a week ago. The North has promised more strikes if the South crosses its maritime border by "0.001 millimeter." Of course the North has an extremely elastic definition of what constitutes that border.

Talking about millimeters amounts to very strong words. The kind that North Korea routinely issues. The real worry for Obama has to be that the North won't stop here, but continue to up the ante. It can keep launching attacks to test the resolve of its enemies. Meanwhile, China will sit on the sidelines, perhaps issuing a polite diplomatic cough every so often, while American diplomats importune it to rein in its frisky charge. China is calling for "peace and stability." Why doesn't it throw in motherhood as well? South Korea's biggest fear seems to be that its bid for the 2022 World Cup might be derailed.

Chalmers Johnson, who died on Saturday, argued that America should never be there in the first place. It's not our problem whether or not South Korea gets its World Cup and our assistance is breeding a form of infantilism in the South. Why should the South be our welfare ward, especially at a moment when the American economy is crumbling?

Pack up the bases. Scram. Let the locals deal with their own problems. It's an understandable impulse and Johnson pointed acutely to the excesses of American empire. But if America pulled out, a vacuum would develop in the region. The optimistic scenario would be that China becomes a benevolent regional hegemon, enforcing order. But the risk--a very big one--is that the whole region would get sucked into war, including Japan. For now America is the pacifier.

For Obama, however, Pyongyang's brinkmanship is a reminder that his presidency could be capsized, not simply by the economy, but also by an unintended war. North Korea may not want a war. But at some point it could provoke one. If Obama wants a real diplomatic coup, maybe he should focus less on the Middle East and more on Asia, which he recently visited. Ending the stalemate between North and South Korea would rank as an enormous accomplishment. So far, Obama himself hardly has any in foreign affairs.