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›› Trump has few options on dealing with North Korea.

When Donald Trump said on Twitter in early January that a North Korean test of an intercontinental ballistic missile capable of reaching the U.S. “won’t happen!” there were two things he still did not fully appreciate: how close Kim Jong Un, the North’s leader, was to reaching that goal, and how limited any president’s options were to stop him.

The ensuing six months have been a brutal education for Trump. Kim’s repeated missile tests show that a more definitive demonstration that he can reach the U.S. mainland cannot be far away, even if it may be a few years before he can fit a nuclear warhead onto his increasingly powerful missiles. But for Trump and his national security team, Tuesday’s technical milestone simply underscores tomorrow’s strategic dilemma.

A North Korean ability to reach the U.S., as former Defense Secretary William Perry noted recently, “changes every calculus.” The fear is not that Kim would launch a pre-emptive attack on the West Coast; that would be suicidal, and if the North’s 33-year-old leader has demonstrated anything in his five years in office, he is all about survival.

But if Kim has the ability to strike back, it would shape every decision Trump and his successors make about defending America’s allies in the region.

Options and downsides

So what are Trump’s options, and what are their downsides?

There is classic containment: limiting an adversary’s ability to expand its influence, as the U.S. did against a much more powerful foe, the Soviet Union. But that does not solve the problem; it is just a way of living with it.

He could step up sanctions, bolster the U.S. naval presence off the Korean Peninsula — “we’re sending an armada” he boasted in April — and accelerate the secret U.S. cyber program to sabotage missile launches. But if that combination of intimidation and technical wizardry had been a success, Kim would not have conducted the test Tuesday, knowing that it would only lead to more sanctions, more military pressure and more covert activity — and perhaps persuade China that it has no choice but to intervene more decisively.

So far, Trump’s early enthusiasm that he had cajoled China’s president, Xi Jinping, to crack down on the North has resulted in predictable disappointment. Recently, he told Xi that the U.S. was prepared to go it alone in confronting North Korea, but the Chinese may consider that an empty threat.

He could also take another step, and threaten pre-emptive military strikes if the U.S. detects an imminent launch of a intercontinental ballistic missile — maybe one intended to demonstrate the potential reach to the West Coast.

William Perry argued for that step in 2006, in an op-ed in the Washington Post that he wrote with a future defense secretary, Ash Carter.

“If North Korea persists in its launch preparations, the United States should immediately make clear its intention to strike and destroy” the missile on the pad, the two men wrote.

But Perry noted recently that “even if you think it was a good idea at the time,” and he now seems to have his doubts, “it’s not a good idea today.”

The reason is simple: In the intervening 11 years, the North has built too many missiles, of too many varieties, to make the benefits of a strike like that worth the risk. It has test-flown a new generation of solid-fuel missiles, which can be easily hidden in mountain caves and rolled out for quick launch.

And the North Koreans still possess their ultimate weapon of retaliation: artillery along the northern edge of the Demilitarized Zone that can take out the South’s capital, Seoul, a city of about 10 million people.

In short, that is a risk the North Koreans are betting even Trump, for all his threats, would not take.

“A conflict in North Korea,” Defense Secretary Jim Mattis said on CBS’ “Face the Nation” in May, “would be probably the worst kind of fighting in most people’s lifetimes.”

Which leads to the next option, the one that South Korea’s new president, Moon Jae-in, talked about in Washington on Friday when he visited Trump: negotiation. It would start with a freeze in North Korea’s nuclear and missile tests in return for a U.S. agreement to limit or suspend military exercises with South Korea.

Xi has long urged that approach, and it won an endorsement on Tuesday from President Vladimir Putin of Russia, after he met with the Chinese leader.

Kim’s self-preservation

As Kim looks around the world, he sees cases like that of Col. Moammar Gadhafi of Libya — an authoritarian who gave up his nascent nuclear program, only to be deposed, with U.S. help, as soon as his people turned against him.

That is what Kim believes his nuclear program will prevent — a U.S. effort to topple him.

He may be right.