My scientific background means that I tend to think that decisions should be evidence based, and be formed after analyzing the information available to whoever is making the decision. But a further point, and one I try to put into my novels, is that decisions involving human activity such as politics or confrontation should relate also to the future consequences. If you are going to make a decision that has adverse consequences, there should be the probability that beneficial ones will significantly outweigh the adverse ones. An interesting point here is that very frequently the adverse consequences can be seen fairly clearly and they are likely to happen, while the beneficial ones tend to rely on hopes. Even an act like buying something falls into this. The immediate adverse consequence is that sum of money is no longer available; the hope is the item will be beneficial. In this case you can probably guess that it will be, but on the other hand when you are young and you buy a used car you can never be sure. There can also be unforeseen adverse consequences. When I purchased my first car I had a mechanic check it out, and I knew the motor would need the piston rings replaced. I factored that into the price I offered, but when the motor was disassembled it was found that when originally assembled, someone had put a bearing in back to front, and the cranckshaft had been ground down. That was an unforeseen adverse effect, particularly on my bank balance.
Taking this to international politics, I believe that one important point is that when a country decides to enter an agreement with others, the other parties can accept that the agreement will be honoured. Doubts as to whether the agreement is worthwhile should be ironed out during the negotiations prior to the agreement being signed. In this sense, it is like a business contract. When one company signs a contract with another company, or person, each side assumes that the other will carry out its obligations. If they do not, they tend to end up in court. If there is absolutely no trust, nobody does any business, and if there is no commerce, everybody ends up the loser. Of course, every now and again someone cheats, and the other parties invariably lose. Occasionally, this can become catastrophic. A possible example of this comes from Kobe steel. Generally speaking, Japanese manufacturing has been praised for its adherence to quality control and quality management, but now it has been reported that Kobe Steel has been selling substandard steel for about a decade. Presumably not all has been substandard, but the problem with steel is that it tends to be structural and deep inside something else of considerably more value, so the ripples will go deep if these allegations are true. If so, this situation is now something of a disaster for Kobe Steel, but it would also be very bad for Japanese commerce as a whole.
It is these unforeseen issues that tend to have a lasting effect, but worse is when one side properly follows its obligations and the other side simply refuses, or decides to pull out of the agreement. The threat of pulling out of an agreement if the other side does not make more concessions is a particularly bad procedure. You get all the concessions you think you can, you agree, then after the other side has started to commit itself, you pull out and demand renegotiations. That, at the very least, leaves a bad taste.
Which brings me to President Trump. Since taking office, he has withdrawn from the Trans-Pacific Partnership (and in fairness, America had yet to sign, so he was entitled to do that), he has withdrawn from the Paris Accord, he has threatened to withdraw from the North American Free Trade Agreement, has signalled that he will withdraw from a trade pact with South Korea, and has now “decertitifed” (whatever that means) a multi-lateral agreement designed to stop Iran from developing nuclear weapons. In the latter case, international observers all agree that Iran is keeping to its side of the deal. Within the US he seems to have been trying as hard as he can to hobble Obamacare, seeing as he cannot abolish it altogether. It is as if he is a serial offender. Iran has apparently signalled to North Korea that it is a waste of time entering into an agreement with the US. Given that Kim can read smoke signals too, that is not encouraging.
Being destructive is easy. Anyone can tear up agreements. The problem then is, what happens next? Maybe Trump does not care, on the grounds that the rest of the world needs the US more than the US needs the rest of the world. I hope that is not what he is thinking, because it is not true.