Correction: An earlier version of this editorial proposed that China be designated as a money launderer. The editorial should have said North Korea.

ASSESSING THE behavior of North Korean ruler Kim Jong Un is necessarily a matter of guesswork. In light of North Korea’s launch Sunday of another long-range rocket, however, our favorite theory is a simple one: Mr. Kim is responding rationally, even shrewdly, to the outside world. The 30-something dictator no doubt noticed that after the regime’s latest nuclear test, on Jan. 6, there was no response other than rhetoric from the U.N. Security Council, China and the United States. Moreover, he surely observed that his provocation served to widen a rift between Washington and Beijing over how to handle him. So why not double down?

The three-stage rocket launched Sunday, which supposedly put a satellite into Earth’s orbit, could also serve as an intercontinental missile. If North Korea has succeeded, as it claims it has, in miniaturizing a nuclear warhead, Mr. Kim could target Hawaii and Alaska, or perhaps even the western U.S. mainland. The threat is not imminent — and yet it is likely to become so if the United States does not devise a more effective strategy for containing and deterring the Kim regime.

President Obama’s policy since 2009, “strategic patience,” has failed. The policy has mostly consisted of ignoring North Korea while mildly cajoling China to pressure the regime. As the supplier of most of the isolated country’s energy and food, Beijing has enormous leverage. But Chinese President Xi Jinping appears even more committed than his predecessors to the doctrine that it is preferable to tolerate the Kim regime — and its nuclear proliferation — than do anything that might destabilize it.

Since the nuclear test, China has been saying that it will support another U.N. resolution on North Korea, but it is balking at significant new sanctions. Instead it calls for “dialogue,” by which it means negotiations between North Korea and the United States. This sounds reasonable; the problem is that talks on curbing North Korea’s nuclear program and missiles have failed repeatedly, and Mr. Kim is now insisting that the regime be accepted as a nuclear power.

What is needed is a return to the only non-military strategy that brought results: sanctions that strike at the regime’s inner circle. Mr. Kim and his cronies are still managing to import luxury goods from China, in spite of a U.N. ban; they still use Chinese banks to do business with the rest of the world. Those links could be curtailed if North Korea, like Iran before it, were designated as a money launderer and U.S. sanctions were slapped on Chinese banks and other businesses that supply weapons and luxury goods.

Pending U.S. sanctions legislation, already passed by the House and scheduled for a Senate floor vote this week, would mandate these steps, while providing the administration with some flexibility. It should pass, and Mr. Obama should sign it. The administration and South Korea have taken one positive step, by announcing formal consultations on deploying an advanced missile defense system in South Korea as quickly as possible. That sensible step had been on hold because of China’s objections.

Both China and North Korea must see that they will pay a mounting price for what, to the United States, should be Mr. Kim’s intolerable steps toward a nuclear arsenal. “Strategic patience” is no longer a viable option.