America’s posture toward North Korea has changed, Trump administration officials insist. Vice President Mike Pence, visiting South Korea, declared that “era of strategic patience is over” and warned the north not to test President Donald Trump’s resolve or the strength of the U.S. military forces in the region.

But what does that mean? Does Mr. Trump really intend to take pre-emptive action against the North Korean nuclear weapons and ballistic missile programs? Or is his saber rattling — moving an aircraft carrier battle group to the Korean peninsula and pointing to his missile strikes in Syria and use of a massive conventional bomb in Afghanistan — merely intended to frighten North Korean leader Kim Jong-un into capitulation? Either way, it’s a dangerous game, for the United States, for both Koreas, for Japan and for China. This decades-long standoff already has one unpredictable, ruthless and reckless leader. It doesn’t need two.

During the campaign, Mr. Trump had a simplistic view of North Korea as a client state of China that could be brought to heel at Beijing’s whim. After a tutorial at Mar-a-Lago from Chinese President Xi Jinping, President Trump has come to the conclusion that “it’s not so easy.” In an interview with the Wall Street Journal last week, he added, “I felt pretty strongly that they had a tremendous power [over] North Korea. ... But it’s not what you would think.” The next day, he tweeted “I have great confidence that China will properly deal with North Korea. If they are unable to do so, the U.S., with its allies, will! U.S.A.” Then on Sunday he tweeted “Why would I call China a currency manipulator when they are working with us on the North Korean problem? We will see what happens!”

If there is any consistent thread there, besides the president voicing whatever pops into his head at any given moment, we’re at a loss to discern it. China can’t control North Korea. Or it can. But we don’t need it to. Or it might if Mr. Trump stops calling it a currency manipulator, which it isn’t.

There are no good options to curtail North Korea’s nuclear ambitions. China can bring economic pressure to bear on the north, but it also doesn’t want to risk a sudden collapse of the Pyongyang government — and the flood of refugees that would pour across its border. We can engage in covert operations to sabotage North Korea’s weapons programs, and a recent string of failures in ballistic missile tests, including one this weekend, suggest we may be having some success at it. But that won’t stop the programs altogether. And military strikes threaten disaster that would make the Syrian civil war appear a minor problem by comparison. North Korea’s forces are heavily dug-in and are capable of inflicting massive damage on South Korea. We cannot contain them with a few airstrikes.

Mr. Trump prizes being unpredictable, but that trait is only likely to make the Kim regime more committed to its nuclear program. The North Korean leadership is reportedly fixated on the case of Libyan strongman Muammar Gadhafi, who gave up his nuclear program voluntarily only to find himself ousted and killed a few years later in a Western-backed revolution. Mr. Trump’s belligerence and volatility only deepen North Korean paranoia and reinforce the logic of its nuclear ambitions.

At one point, Mr. Trump suggested he could solve the whole problem if he could sit down and have a sandwich with Mr. Kim (an idea the official Twitter account of the North Korean news service called the “ignorant daydream of a deluded simpleton”). The North Korean situation isn’t a run-of-the-mill misunderstanding, and it isn’t an opportunity for Trumpian deal-making. Talking tough won’t strengthen the American position; it will make Mr. Kim dig in deeper.

The weekend came and went without a nuclear test by North Korea, but we would caution the Trump administration not to read that as a validation of its strategy. Speculation that the regime intended time the test to the birthday of Mr. Kim’s late grandfather may simply have been incorrect. Regardless, there is little reason to doubt that the regime will go forward with another test soon in its quest to build a smaller and more powerful warhead. We need to be in a position to respond with something more than military threats.

There are signs that China’s leadership may be willing to engage in a range of diplomatic strategies with the United States and its allies to contain the North Korean threat. We can only take advantage of that if Mr. Trump trades his bellicose rhetoric for calm, steady determination. Mr. Kim appears to believe he is already in a life-and-death struggle with the United States. The last thing we need to do is to encourage him.