For a long time, President-elect Donald Trump has long made it clear that he views unpredictability in foreign policy as a virtue and a strength.

At a recent rally in New Hampshire, Trump promised his supporters a foreign policy that neither they nor America’s enemies could ever anticipate. “I want to be unpredictable,” Trump declared. “We want to go in, we don’t want them to know what the hell we’re doing. We have to go in, and people love it when I say that.”

In some cases, the idea of unpredictability could conceivably be sensible. For example, in October, Mr. Trump had this to say about the campaign to retake Mosul:

You take a look at Mosul and the biggest problem I have with the stupidity of the foreign policy, they take a lot of them in Mosul. We have announcements out of Washington and Iraq. We will be attacking. Why can’t they do it quietly and do the attack and make it a sneak attack and after the attack is made inform the American public that we have knocked out the leaders and have a tremendous success. People leave. Why do they have to say we are going to be attacking Mosul in four to six weeks. How stupid is our country?

In fact, Mr. Trump was wrong from every perspective about Mosul, according to experts. But whether or not surprise would have been preferable in a military sense in Mosul, Trump deployed the same idea in a context where it is clearly inappropriate and dangerous. When asked specifically about what he would do if Russia invaded the Baltic states, he refused to say whether he would come to their aid. He seemed to have gotten fixated on the idea that it’s a bad idea to announce our intentions in advance after his criticism of the US military for speaking about the planned campaign to retake Mosul a few days earlier.

I don’t want to tell you what I’d do because I don’t want Putin to know what I’d do. I have a serious chance of becoming president and I’m not like Obama, that every time they send some troops into Iraq or anyplace else, he has a news conference to announce it.

Unpredictability has no application here. The whole point of NATO is to keep the peace by making sure allies and adversaries in Europe know exactly what we will do if a NATO country is attacked, namely, what we said we will do in Article 5 of the North Atlantic Treaty:

The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.

When pressed by the interviewer, Mr. Trump suggested that another reason for his refusal to speak clearly, in addition to the supposed benefits of ambiguity, was the failure of NATO allies to pay their bills, i.e., to meet NATO’s defense spending goals, which are based on a percentage of GDP. Leaving aside the fact that Estonia, one of the states the interviewer asked about, is meeting its defense spending goal, it seems to me that even if the Baltic states, for example, paid little or nothing, and even if we didn’t care at all about the Baltic states for their own sake or about the rest of the world for its own sake, our promise to allies and adversaries alike about the consequences of an invasion of the Baltics is incredibly beneficial to us, because it keeps the peace. Anyone who thinks Russia is not interested in territorial expansion or in dominating what it calls the “near abroad” has plenty of real world examples to set him straight. The fear is that even if, in the end, the United States would honor its treaty commitments, Mr. Trump’s statements raise the risks of war by increasing the chance of a miscalculation—a wrong belief that, as Mr. Trump has now suggested, we would not do what we say.

A similar issue is raised by Mr. Trump’s ill-advised (in my view) conversation with the President of Taiwan. Even if the incoming Trump administration plans to make a change in the United States’s longstanding “one China” policy, it’s not something to be done without careful deliberation and then scrupulous stage management once the decision has been made. Here, it’s really unclear from the coverage whether there was any conscious decisionmaking, and the stage management was inept. Some accounts suggest that there’s nothing to see here: Trump’s intention was just to accept a congratulatory phone call. Others claim the call was deliberate and, in fact, planned over a long period of time. In any event, after China’s low-key response to what it has to see as a provocation, Mr. Trump decided it would be best to inflame things by attacking the Chinese via Twitter:

https://twitter.com/realDonaldTrump/status/805538149157969924

https://twitter.com/realDonaldTrump/status/805539770864693253

There’s a lot to worry about domestically, but however effective unpredicability and shooting from the hip was for Mr. Trump in his past life, it’s time for him to take advice from experts in the State Department and elsewhere in the government.