WASHINGTON -- North Korea's recent temper tantrum over U.S.-South Korean military exercises and its threat to pull out of its upcoming summit with President Trump are signs that Trump's North Korea strategy is working.

Over the past several months, Trump has boxed in Kim Jong Un. First, he ramped up economic pressure on Pyongyang while making clear that, unlike his predecessors, he was willing to take military action. Yet when Kim offered to meet face-to-face, Trump shocked everyone (probably including Kim) by reportedly accepting on the spot. Instead of rejecting the offer, or using it as a bargaining chip to elicit concessions, Trump said "yes" and put the two nations on a faster track to nuclear negotiations than anyone had anticipated.

Then, the president began shaping the parameters of an agreement -- starting with making clear what kind of deal he would not cut. The North Koreans want a nuclear deal like the one President Barack Obama gave to Iran: sanctions relief up front, billions of dollars in cash, a weak inspection regime and sunset clauses on the back end. By withdrawing from the Iran deal last week, Trump sent Pyongyang a crystal-clear message: I don't cut deals like that.

He then used his senior officials to lay out the parameters of the kind of accord he would cut. Kim wants to get paid for the promise of denuclearization. Appearing on "Face the Nation," national security adviser John Bolton played the bad cop and explained that that is not happening. Trump will only pay for actual denuclearization. The president, Bolton said, is looking for "a manifestation of the strategic decision to give up nuclear weapons [that] doesn't have to be the same as Libya but it's got to be something concrete and tangible it may be that Kim Jong Un has some ideas and we should hear him out."

While Bolton set expectations for denuclearization, Secretary of State Mike Pompeo played the good cop and held out the twin carrots of security and prosperity if Kim agrees. "If North Korea takes bold action to quickly denuclearize," Pompeo said, "the United States is prepared to work with North Korea to achieve prosperity on par with our South Korean friends." That stunning offer is deeply destabilizing for Kim. If he goes to a summit with Trump and refuses to accept a deal that provides his country with prosperity on par with South Korea, then he can no longer blame the West for the misery of the North Korean people.

In other words, Trump and his national security team have put Kim in a corner, offering him peace, security and prosperity, but only if he first denuclearizes completely, verifiably and irreversibly. Little wonder that North Korea is lashing out.

Kim might be looking for a pretext to get out of his meeting with Trump, and the military exercises provide a perfect excuse.

He may also be testing Trump to see how badly he wants the summit. Or he may be trying to drive a wedge between the United States and South Korea in advance of the talks. He knows South Korean President Moon Jae-in is deeply invested in his "Sunshine Policy" with Pyongyang. If the North threatens a little rain, perhaps the South -- which desperately wants the summit -- will pressure Trump to cancel the military exercises or be more flexible at the bargaining table.

Trump needs to show Kim that he won't respond to threats by refusing to call off the exercises. Through back channels, he needs to reaffirm his willingness to provide North Korea with security and prosperity in exchange for immediate denuclearization but also make clear that if North Korea refuses, the alternative is not the status quo. Sanctions will be ramped up, and military action is possible. Above all, Trump should take North Korea's recent outburst as a signal that Pyongyang is feeling the heat.

A cornered animal roars, precisely because it is cornered. Stand firm, Mr. President, and don't let up the pressure.