If North Korea launches a nuclear warhead-armed ballistic missile over the Pacific Ocean, the U.S. should attempt to shoot it down and then push for a naval blockade of North Korea.

The concern here is real.

In recent weeks, North Korean officials have hinted that they may launch just such a test. As one Pentagon official told reporters, Tuesday, "I would fully expect if [Kim's] telling us he’ll do it, he’s going to."

The threat is exacerbated by two other factors. First, the recent tunnel collapse at a North Korean nuclear test facility may motivate Kim Jong Un to believe an atmospheric nuclear test is necessary to save face. Second, as President Trump prepares to visit South Korea next week, Kim may want to send a uniquely aggressive message.

Regardless, if Kim acts, the U.S. cannot sit idle.

For a start, whether or not the warhead actually detonated, a successful nuclear-armed ballistic missile test would advance North Korea's program significantly. As with the Soviets in 1957, each test moves the needle closer to a credible capability. For that reason, U.S. policymakers must attempt to shoot down the missile.

But what if North Korea succeeded in any test?

Well, if the North successfully detonated a nuclear warhead over the Pacific, the crisis would immediately enter an unprecedented state. That's because such a test would force the international community to accept that North Korea had achieved nuclear-weaponized competence.

To confront that challenge and deter other nations such as Iran from following in North Korea's example, the U.S. would have to push for a major escalation in its diplomatic-military strategy. A naval blockade seems well-suited here in that it would exert both physical and psychological pressure on Kim Jong Un's regime.

At the United Nations, the U.S. could warn that absent a resolution for a blockade, it would massively ramp up its long-term military presence in the region and introduce wide-ranging sanctions on financial entities that support Kim's economy. Such action would seek to alter the strategic calculus of President Xi's government in Beijing. At present, China believes it can achieve a status quo in which North Korea attains a nuclear weapons capability and the U.S. accepts China's regional hegemony.

The U.S. must disabuse China of this optimism.

Ultimately, while U.S. policy should be focused on effective diplomacy, we must accept that North Korea launching nuclear weapons into the Pacific Ocean is intolerable.