Aside from the president’s rhetoric, little suggests that war on the Korean Peninsula is at hand.
The warnings from Mr. Trump — and equally bellicose responses from Mr. Kim — have increased tensions. But left unclear are the circumstances under which the United States might be willing to use military force. Would it shoot down a North Korean missile that was being tested near Guam? Would it launch an attack to try to destroy the North’s program to develop intercontinental missiles and the nuclear warheads they would carry? Would it act pre-emptively or reserve the use of force to deter an attack on American territory or on the United States’ allies?
Here are some of the possible military scenarios, and the consequences that military and diplomatic officials say they might spawn.
Taking Out a Single Missile
A preventive strike on one of Mr. Kim’s missiles is just one of several scenarios that military experts say could play out during an escalating conflict between North Korea and the United States in the coming weeks or months.
With Mr. Trump’s order given, American aircraft would take to the skies or perhaps Tomahawk cruise missiles would be launched from the decks of a destroyer near the Korean Peninsula, streaking through the sky at speeds of up to 550 miles per hour toward the Korean missile’s garrison.
What happens next is at the heart of the unease inside America’s military command, where the use of force against North Korea has long been seen as a last-ditch option, to be used only if diplomatic efforts fail.
If he gives the go-ahead, Mr. Trump would be betting that a single strike would force Mr. Kim to accept that his arsenal had been diminished while withdrawing from the brink of a confrontation with his Asian neighbors and the United States.
But military officials fear that Mr. Kim might misinterpret such a strike, seeing it not as a single event but as the first wave of a broader assault on his government, and lash out with a barrage of artillery and conventional missiles streaming toward Seoul or Tokyo. Or Mr. Kim could order his military to march across the demilitarized zone separating the two Koreas.
In a less risky variant of this option, the United States could use the Terminal High Altitude Area Defense, or Thaad, antimissile battery in Guam to shoot down any North Korean missile tested near that territory. That action could be presented as purely defensive, but the credibility of the Thaad system would be undermined if it missed.
Striking Nuclear Missiles
If Mr. Kim attacks first, perhaps by firing several missiles at the American military base on Guam, Mr. Trump would have to decide how to respond. Inside the high-security Situation Room at the White House, the president could order a surprise, all-out assault on North Korea’s missile fleet and its nuclear weapons arsenal.
The sudden attack scenario could begin like the single strike, but much larger. Tomahawks could launch from dozens of destroyers positioned on both sides of the peninsula, blasting multiple sites across the North Korean countryside.
At the same time, strike aircraft based at the Guam air base, in Japan, and on aircraft carriers in the region could take off, risking the threat of attack from North Korea’s ground-to-air defenses as they seek out the country’s armaments, some of which are believed to be hidden in well-fortified underground bunkers. Stealth bombers, which would be refueled in flight, could also take off from the United States.
William Perry, who served as secretary of defense in 1994 when President Bill Clinton considered a plan to destroy a North Korean nuclear reactor, said the government’s weapons are even more deeply protected now.
“We had to assume that North Korea would make a strike on South Korea in some way, and if they were to use their artillery to attack Seoul, they could kill tens of thousands before we could stop them,” Mr. Perry said. “The price was very high then, but the price today would be very much higher.”
American military officials are deeply concerned that they would not be able to “find, fix and finish” the North’s entire arsenal of long-range missiles and nuclear weapons, leaving a significant risk of a “leaker” or a “bleeder” — one or more missiles with warheads that may or may not be able to carry out a nuclear strike against the United States or its allies.
It would be up to the United States missile defenses to knock out leakers. The Thaad battery, which is stationed in South Korea, could be used to defend South Korea.
Missiles headed for the American mainland might be intercepted by the Ground-Based Midcourse Defense based in Alaska and California, which has a spotty record, although its most recent test, in May, was a success.
Preparing for All-Out War
Chief among the concerns of military experts about the first two scenarios is the possibility of sparking all-out war on the Korean Peninsula.
That could lead Mr. Trump to embrace a different military scenario — the slow-paced buildup to an all-out ground invasion of North Korea.
It would begin with evacuations of Americans and allies in South Korea. Moving them out of harm’s way would be an enormous logistical operation, perhaps leaving time to see whether economic sanctions had any impact on the North’s behavior and for diplomacy to work.
During the same period, ships would begin steaming to the Korean Peninsula from Hawaii and elsewhere as the military pre-positioned additional artillery, counter-battery radar and other assets. The American troop presence could ratchet up to levels not seen in a foreign country since President George Bush sent more than a half-million troops to the Middle East in 1990.
The buildup would abandon any element of surprise, but it would be a message of deterrence for Mr. Kim against a first strike. It would also give the American president the option of taking limited action while trying to discourage North Korea from raising the stakes and tilting the battlefield to the United States’ advantage if he did.
Military officials worry, however, that Mr. Kim could use the time to move his long-range mobile missiles around to make them harder to strike. And he could interpret the United States buildup as the beginning of a campaign to take down his government — raising the prospect that he would strike first, either with conventional or nuclear forces.
And if all-out war on the peninsula ensues, military officials say the result would be devastating, potentially leading to the deaths of hundreds of thousands of people even if nuclear weapons are not used, something that they say is hardly assured.
American military officials are nearly unanimous in their belief that the military options are complicated, difficult and dangerous. Mr. Trump has other tools at his disposal to confront North Korea.
In 2014, President Barack Obama ordered cyber- and electronic-warfare attacks on the North’s missile program. For nearly three years, the failure rate of the North’s missile launches soared, though it is not clear how many of those failures can be attributed to the American effort, and their success has increased recently. At any rate, the cyberattacks have not slowed the North Korean program sufficiently enough to avert the current crisis.
The United States government could also turn to other covert means to change the North Korean government. In July, Mike Pompeo, the C.I.A. director, said: “As for the regime, I am hopeful we will find a way to separate that regime from this system.” He added quickly that he was not advocating “to make happen tomorrow.”