By Judith MillerWriter/Scholar, The Manhattan Institute/FOX News Contributor

North Korea sure knows how to get President Obama's attention on Memorial Day. And it's not by extending an unclenched fist.

While its first nuclear test in 2006 was by all accounts a dud, Pyongyang's test this morning at 9:54 a.m. GMT apparently yielded a more than respectable blast of between 4 and 20 kilotons, which could be larger than the bomb that leveled Hiroshima.

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Make no mistake about it: China must now act.

That officially makes North Korea the ninth member of the world's nuclear club - and the only state to have signed and withdrawn from the Nuclear Non-Proliferation Treaty, an international dike against non-proliferation now springing so many leaks that it's in danger of collapsing.

What to do now? The expected denunciations were quick in coming. They will be echoed again and again today at the United Nations Security Council, which meets to discuss what President Obama has called North Korea's "violation of international law," and "threat to international peace and security." Such provocations, he added, "will only serve to deepen North Korea's isolation."

The White House statement, however, was short on specifics. Stating the obvious -- that North Korea's tests "warrant action" -- President Obama said the U.S. would "continue working with our allies and partners in the Six-Party Talks as well as other members of the U.N. Security Council in the days ahead."

But all "partners" are not equal. China is the key to stopping North Korea's nuclear bomb development and proliferation activities. Just as Obama must cajole Beijing into supporting tough sanctions against another nuclear proliferation wanna-be -- the Islamic Republic of Iran -- the administration must persuade China to do what it has so far resisted -- tell North Korea to cease and desist its nuclear bomb program and implement the pledges it has made and repeatedly broken to dismantle its programs.

Make no mistake about it: China must now act. It supplies between 80-90 percent of North Korea's power, 90 percent of its crude oil and all of its diesel fuel. Between 70 and 80 percent of North Korea's food imports come through China. And while ailing autocrat Kim Jong Il clearly doesn't care if his people starve, he might care if China nixes his apparent plans, as reported in The Wall Street Journal, to have his brother-in-law and third son succeed him.

This argument is made convincingly by Thomas C. Reed and Danny B. Stillman in their terrifying new book, "The Nuclear Express: A Political History of the Bomb and its Proliferation." China, they maintain, is the "wild card," the only country with true leverage over North Korea.

A little nuclear history is in order here. Washington, they note, has tried myriad strategies to rein in Pyongyang since the end of the 1980's, when it developed enough fissile material for one or two atomic bombs. (It now has enough plutonium for an estimated five or six.) Washington has considered but always, wisely, rejected military action -- given the American troop presence in South Korea and the vulnerability of our South Korean ally.

In spring of 1994 under President Clinton, Reed and Stillman note, then Defense Secretary William Perry developed plans to bomb North Korea's plutonium reaction, but concern that North Korea would invade or attack South Korea led to the shelving of those plans.

North Korea tested its bomb, a one kiloton dud which achieved only 4 percent of its yield design, say Reed and Stillman. But while a technical failure, the test was a political success. It prompted the U.S. to return to Six Party Talks. This, John Bolton, the former U.S. ambassador to the U.N. argued only five days ago, "gave Kim Jong Il cover to further advance his nuclear program."

In 2006, then former Defense Secretary Bill Perry and fellow defense analyst Ash Carter urged President Bush in an essay in The Washington Post to "immediately make clear its intention to strike and destroy the North Korean Taepodong missile before it can be launched." "Should the United States allow a country openly hostile to it and armed with nuclear weapons to perfect an intercontinental ballistic missile capable of delivering nuclear weapons to U.S. soil? We believe not," the authors argued. Ash Carter is now President Obama's appointed Undersecretary of Defense for Acquisition.

But the Bush administration wound up doing what its predecessors did -- negotiate again with Pyongyang, through Six Party Talks. In 2007, Washington agreed to supply North Korea with 1 million tons of fuel oil in exchange for North Korean pledges to dismantle its nuclear facilities. A year later, North Korea destroyed the cooling tower of its reactor, but quickly reverted to its previous tactics of signing and stopping dismantlement, this time allegedly because of a dispute with Washington over how its 18,000-page-list of atomic-related activities would be verified.

In April, North Korea launched a Taepodong-2 missile, prompting more international condemnation. Its national pride wounded and another pretext provided, North Korea vowed more escalation -- a second test, which it has now conducted.

North Korea says it wants direct talks with the U.S. and no more sanctions. The Obama administration seems determined to return to the trap of six party talks, which Bolton, among others, calls "a charade" that reflects "a continuing collapse of American resolve." Bolton warned further, as recently as last week, that U.S. acquiescence to a second North Korean nuclear test will "likely mean that Tehran will adopt Pyongyang's successful strategy."

Fearing some serious economic sanctions or perhaps even more aggressive reprisals, Pyongyang has taken out some additional insurance -- it is about to put on trial two American reporters on trumped up charges. The fate of these reporters seems to hang in the nuclear balance as well.

But since there seems to be no viable military alternative to diplomacy, the Obama administration should play the card it might have -- China. Beijing can command North Korea's attention in a way that Washington cannot. To date, China has been reluctant to punish North Korea, fearful that the ugly regime might collapse and cause chaos or reunify with South Korea. But with so much at stake, Obama must see who our true nonproliferation friends are.