There was a time, within the recollection even of the very young, when newspapers could print the public statements of an American President without first deciding which words must be hidden from children. This is not to pretend that American political speech was ever distinguished by Attic refinement. It is only to observe that a President once understood that private foulness of speech and a declaration of foreign policy belonged in different categories.

Donald Trump has now been reported as telling Fox News: “If Oman gets in the way, we’ll bomb the shit out of them.” The wording matters. This was not a sentence overheard after dinner or an intercepted remark made in the heat of an argument. It was an on-record threat by the President of the United States to attack a country that has allowed American forces to use its military facilities and has spent decades assisting American diplomacy in the Gulf.

One may dislike the false decorum with which states have traditionally announced their murders. I do not deny that a correctly punctuated communiqué can precede an act of appalling violence. Yet decorum had at least one useful function. It compelled rulers to formulate a case that could be examined by their legislatures and allies. Mr Trump’s obscenity dispenses with even that small restraint. He does not offer a legal ground for attacking Oman or identify any Omani act that could amount to aggression against the United States. He says only that Oman must not “get in the way”.

This is the language of arbitrary power in its purest form. A Government announces an objective, another state pursues its own negotiations, and the second state is threatened with bombardment because its independence has become inconvenient. The question is no longer whether Oman has violated a rule known in advance. It is whether Oman has displeased the man who happens to occupy the White House.

The threat is especially revealing because the American policy with which Oman is allegedly interfering has failed on its own terms. The sixty-day period allowed for an agreement with Iran has expired. The Strait of Hormuz remains largely closed, the American naval blockade is again in force, and the nuclear discussions appear to have made no substantial progress. Mr Trump nevertheless demands that Iran raise a “white flag of surrender” while assuring Fox News that he has no timetable and is in no hurry. Surrender is apparently urgent, though obtaining it can wait indefinitely.

The June memorandum was supposed to provide a way out of the war. Instead, it postponed the central dispute. Its language did not settle who would control passage through the Strait or on what terms ships could use it. Iran later attacked vessels moving through channels it regarded as unauthorised, the United States retaliated, and the supposed ceasefire was soon recognised as dead. A document drafted to stop a war had left unresolved the question most likely to restart it.

Any conveyancer of moderate experience will recognise the method. The parties wish to complete, an awkward clause is left for later, and everyone congratulates himself on having preserved the transaction. Later then arrives in the form of litigation. In ordinary private business, the parties lose money and the lawyers open new files. When the transaction concerns warships and a passage through which much of the world’s energy supply must travel, the consequences are less easily confined to a set of chambers.

The safeguards that delay an agreement are not always bureaucratic fat. Some are the connective tissue that allows the arrangement to bear weight once events begin pulling against it. The American Administration treated agreement on the most important disputed waterway as a detail that could be finessed. It has now discovered that an agreement without an agreed meaning is not a peace settlement. It is an interval during which both parties prepare their competing interpretations.

The conflict has therefore become an economic contest of endurance. Washington is betting that its blockade and sanctions will force Tehran to yield. Tehran is betting that control of Hormuz will allow it to survive longer than American tolerance of higher fuel prices and diminishing weapons stocks. Neither side needs legal sovereignty over the Strait to impose enormous costs on persons who took no part in beginning the war. They need only enough military power to prevent everyone else from using it safely.

Mr Trump has proposed to simplify the legal problem by declaring the Strait American territory. The claim has about the same relationship to international law as a presidential announcement that the English Channel belongs to the State of Florida. The narrowest part of the Strait lies between Iran and Oman, and the law of the sea preserves rights of transit through it. An American President cannot acquire the territorial waters of foreign states by putting a notice on Truth Social.

The claim is absurd, but the power beneath it is real. Mr Trump’s argument, stripped of decoration, is that the United States can control movement through the Strait and may therefore call the Strait its own. Iran advances a parallel argument from its geographical position and military capacity. The legal claims of both sides are defective. Their weapons nevertheless allow them to behave as if law were merely the language used by weaker states when complaining.

There is some dispute about what Oman is supposed to have done. According to the reports presently available, Muscat has been negotiating separately with Tehran over an interim arrangement for reopening Hormuz. The Financial Times has reported diplomatic hopes that an Omani agreement might provide a bridge back to the June framework, perhaps allowing Washington to lift the blockade in return for acceptable navigation terms. It requires an unusually disordered conception of diplomacy to threaten the intermediary for attempting to obtain the result that one publicly claims to desire.

Nor is this the first threat. Mr Trump said in May that Oman would have to “behave” or be blown up. The second threat can no longer be dismissed as a momentary eruption. It is becoming a method of government. An ally remains useful only while it immediately produces the desired answer, and any exercise of independent judgment becomes proof that it is obstructing the United States.

Oman’s independence is what makes its diplomatic service useful. It has military and commercial relations with the United States while retaining channels into Iran. Because it is not just an American messenger, Tehran may listen to what it carries. Threatening Oman while relying on its mediation is rather like burning a bridge to encourage the messenger to walk faster. The immediate display of force consumes the instrument needed to secure the stated object.

It is true that Hormuz is of great commercial importance. A large share of the world’s oil and liquefied natural gas normally passes through it, and its obstruction imposes costs on persons who had no voice in this war. Iran’s attempt to extract control or payment from shipping may be unlawful and extortionate. None of this gives the United States a licence to attack Oman. A dispute with Iran cannot manufacture an American jurisdiction over the foreign policy of every neighbouring country.

The market, being less interested in presidential dignity than in getting goods delivered, is already making other arrangements. Saudi Aramco is reported to be using transfers near Fujairah and diverting crude towards Yanbu on the Red Sea. These alternatives have costs and their own dangers, especially where shipping must approach the Bab al-Mandeb. Even so, commerce will route itself around political failure where it can. Governments may continue arguing about sovereignty while the persons who require oil find another pipe.

Oman is not an enemy that Washington has suddenly discovered on the map. The United States has enjoyed access to Omani ports and airfields under defence arrangements whose origins go back to 1980. Oman has been useful because it maintained channels that Washington repeatedly needed. If the reward for such cooperation is a presidential threat of destruction, every Arab government will make the proper entry in its ledger. American protection is conditional on complete obedience, while American obligations disappear whenever obedience is withheld.

This is not how a durable predominance is maintained. Even a satrapy must receive something in exchange for submission. If it may be threatened as freely as an enemy, the prudent satrap will begin looking for another patron. The Gulf governments need not admire Iran before understanding the lesson. Still less must they admire China before deciding that a quiet arrangement with Peking may be safer than friendship with a Washington that conducts diplomacy in four-letter explosions.

The British position deserves closer attention than it is likely to receive from the British Government. Oman was not, in the strict constitutional sense, a British colony. British influence was nevertheless so extensive that the distinction often meant less in practice than it did on paper. The modern relationship is not merely sentimental. Britain and Oman concluded a Defence Co-operation Agreement in 1994, amended it in 2016, and signed a further Joint Defence Agreement in 2019. Britain also maintains military facilities at Duqm and has described Oman officially as one of its most important partners.

I cannot say from the published material that the Joint Defence Agreement imposes an automatic obligation comparable to Article 5 of the North Atlantic Treaty. Its full operative terms do not appear to have been made public. That uncertainty does not relieve ministers of their political duty. A country cannot proclaim an enduring commitment to Omani security and maintain a strategic base on Omani territory, then treat an American threat to bomb Oman as an embarrassing disturbance at luncheon.

The Government should state plainly that no British facility will be used in an attack on Oman. It should also withdraw British assistance from the present American war unless and until Washington renounces the threat. This would not be a declaration of hostility towards the United States. It would be the minimum conduct required of an independent country that claims to respect international law and honour its defence relationships.

There is a further absurdity. American military personnel use Omani facilities, though I have found no satisfactory public evidence for the claim that several hundred are permanently stationed there. The number may vary with operations, and much of the arrangement concerns access rather than a declared American base. Even so, the presence of American servicemen and logistical personnel is not seriously in doubt. Does the proposed bombardment include the facilities from which the United States itself operates? Will the guests be evacuated before they attack their host, or are they to trust that the President’s target selection is more exact than his language?

The uncertainty extends to the supposed diplomacy with Iran. Mr Trump claimed on Monday that Washington had established a direct backchannel to the Islamic Revolutionary Guard Corps. The IRGC promptly denied that any such talks were taking place. I have no independent basis for deciding which statement is true. It is nevertheless remarkable that, on the day the formal arrangement expired, the two governments could not agree in public whether they were speaking to each other at all.

It would be easy to attribute the whole performance to the decay of one elderly man. Mr Trump’s speech invites the conclusion. His public performances have become repetitive and increasingly detached from any evident chain of reasoning. Yet I am a lawyer, not a physician, and I have no clinical evidence on which to diagnose senility. I can say only that his conduct resembles the rambling aggression of a man whose judgment has failed, and that his earlier career does not suggest an intellect from which the decline began at a very great altitude. The personal explanation is also too convenient. Mr Trump has not carried on this war alone. The executive departments obey his orders, while Congress supplies the means. The larger American governing class has allowed the performance to continue for six months. If its members believe him incapable, their acquiescence is a constitutional betrayal. If they believe him capable, then his conduct must be treated as the public expression of a policy they have accepted.

On the evidence presently available, that policy appears to extend beyond preventing Iran from acquiring nuclear weapons. There has been little evidence of sustained negotiation on the nuclear question since June. The actual bargaining now concerns the Strait and the economic pressure applied to Iran. Six months into the war, its operational centre is a passage barely twenty-one miles wide. The declared purpose remains nuclear disarmament, while the machinery of the conflict has moved elsewhere.

The policy may be to break Iran as an effective regional power while compelling surrounding states to submit their diplomacy to Washington. Disorder throughout the Levant and the Gulf is not necessarily an accidental consequence. It may be the condition from which American and Israeli supremacy is expected to emerge. Oman becomes a prospective target because genuine mediation requires independence from the belligerents, while the American policy now permits no such independence.

I cannot prove that every consequence has been planned in advance. Governments are capable of producing catastrophe through stupidity as well as design, and the present Administration does not require a conspiracy to explain its blunders. Yet the continued support of the American political class makes it impossible to dismiss each outrage as a personal eruption. Mr Trump may supply the vulgarity, but an entire system supplies the aircraft and accepts the governing assumptions.

The disregard for institutions is not confined to the drafting of the June memorandum. The Administration repeatedly treats standing arrangements as dispensable impediments and personal access as a substitute for public capacity. A neutral mediator is valuable until its neutrality produces an inconvenient answer. A professional diplomatic service is tolerated until a relative or favourite can go around it. Military preparation is maintained until the President’s personal feelings towards a foreign ruler make preparation appear unfriendly.

This practice can look efficient for a time. Decisions move quickly and the cumbersome persons who remember earlier promises are excluded. Yet a state that transfers its diplomacy into personal relationships also transfers its continuity into private hands. The favoured envoy eventually leaves and takes his contacts with him. The files may remain in the Department of State, but the effective machinery has become the property of whoever last had the President’s ear.

For those who wish to see the strategic collapse of the United States, the result is excellent news. American power has rested in part on a belief that cooperation with Washington provides more security than danger. The threat against Oman reverses that calculation more effectively than any Iranian propagandist could have hoped. It tells every ally that past service creates no claim, and that independent judgment may be punished as if it were an act of war.

Nor can material abundance indefinitely repair the damage. Mr Trump has dismissed concerns about the consumption of American munitions as “peanuts”, but weapons used in one theatre are unavailable in another. Industrial capacity can be expanded only with time, while confidence cannot be ordered from a factory. The United States is spending its physical reserves and its alliance credit together. One may be replenished more easily than the other.

The crassness may bring the collapse sooner than a more coherent policy would have done. A competent imperial administration conceals domination beneath rules and reciprocal courtesies. Mr Trump removes the covering and shouts the arrangement into a television microphone. The old diplomatic machinery remains standing, much as an abandoned solicitor’s office may retain its brass plate after the files have been removed. Oman is still answering the telephone, but it has now been warned what may happen if the answer is not agreeable.