This is probably advice Donald Trump should have considered before ordering the assassination, by a drone, of General Qasem Soleimani, the force commander of Iran's Islamic Revolutionary Guard Corps last Friday. We can take it that Soleimani was an effective military and political leader, whose death would weaken Iran, a nation that is refusing to bend to America's will that it not develop nuclear power, let alone nuclear weapons.

International law is ambiguous on the legality of assassination as an act of war, particularly when no war has been declared. It can be argued that such an act authorises retaliatory assassinations, well away from the theatre of battle, and sometimes not of great military or political figures on the other side, deplorable as that might be, but of American soldiers anywhere, or Americans anywhere - or, sometimes, the soldiers or civilians of American allies anywhere, even when they are innocently travelling on a train with their families. It is generally thought that the soldiers and citizens of nations such as the US, or its allies such as Australia, are at a disadvantage when these seem to become within the rules of engagement.

This is something that the United States ought to have learnt by now. In my lifetime, for example, it has sponsored or winked at the assassination of leaders such as Ngo Dinh Diem in South Vietnam, Salvador Allende in Chile, and Muammar Gaddafi in Libya, and took several failed potshots at Fidel Castro of Cuba. Not one of these efforts succeeded in the purposes intended - in most cases it had exactly the opposite effect.

With Diem and Allende, for example, the very cynicism and amorality of the attacks seriously undermined the moral basis of American involvement in the relevant region, such as it had been, and mightily empowered critics and enemies. Conniving at the assassination of Gaddafi, or invading Iraq so as to impose "regime change", did not make life safer or more stable and predictable for Libyans or Iraqis. Indeed it caused hundreds of thousands of deaths, inspired new and more murderous enemies of the Western alliances, and destabilised most of the neighbours, requiring progressively more and more allied military intervention.

Hunting down and "taking out" some terrorist leaders, such as Osama bin Laden, may not fit into the same category as targeting and taking potshots at foreign politicians and generals, even if there is at least the argument that a diversion of military resources into revenge rather than defeat of the enemy's forces is often counterproductive. Not only does it have a tendency to make martyrs of the enemy's leaders, but it comes to justify asymmetrical tactics, including the use of improvised explosive devices, attacks on civilians, and, often down the track, suicide bombing and random attacks, anywhere, on civilians or symbols of the state in question. To this day, Osama bin Laden - a revolutionary leader whose charisma and effectiveness were honed by American support of the mujahideen while it was helping rid Afghanistan of the Russians - is a hero to many in the third world.

One might imagine that these were points that would have been made to Donald Trump by his own advisers, and by America's allies, were Trump disposed to listen to the former or consult the latter. As with his giving effective authorisation for an invasion of Syria by Turkey, the assassination took almost everyone by surprise, including the Australian political and military establishment. Our very cautious response since has been focused rather more on ensuring the safety of Australian soldiers and sailors in Iraq, in the Persian Gulf, and in the immediate region than on making any fresh commitment to going all the way with an increasingly erratic and emotional US President, whose tactics and strategy are a mystery even to many of his own advisers.

Trump has been impeached on charges of attempting to use American aid improperly to achieve a personal partisan purpose - blackmail to get dirt on a possible Democrat rival. There are some who think his latest military adventure in Iran and Iraq is also designed for a political purpose - in this case a distraction from the embarrassments and divisions of the forthcoming trial. Not to mention the election in November, after he is acquitted of the impeachment charges by Republicans in the US Senate.

The surgical take-out of Soleimani and a few of his staff by drone at Baghdad's airport gives Trump a chance to look "tough" and uncompromising. Americans typically rally around the flag when the nation is engaged in conflict - and those who make politics or promote disunity will have their patriotism impugned, not least for being petty and political rather than standing foursquare behind the American flag.

There are others who fear or suspect that Trump is playing tough so as to distract attention from the fact that his strategy to contain North Korea, and to force it to disarm all of its nuclear weapons, does not appear to be going well. Nor, yet, does his other planned foreign policy triumph of "winning" the trade war against China. With each, he is promising that there is light at the end of the tunnel, with, in effect, the troops coming home by Christmas. Each battle has involved a good deal of threats and bluster, followed by more conciliatory tones, followed by declarations that he has reached an understanding with the other side - a major advance which has made all of the effort worthwhile. It has been much the same with Iran, even if he has carried out his campaign promise to repudiate a multilateral agreement - negotiated with most of the European Union as well as his predecessor, Barack Obama - which involved a lifting of sanctions against Iran and a promise of assistance in its development of peaceful nuclear power, in exchange for a promise of stopping any activity designed to develop a nuclear weapon, and allowing international inspection to make sure this was happening.

Iran had complied, more or less, with the deal, at least until Trump - who had attacked it as too weak - repudiated it. Then it announced it would resume research, and the development of fissionable material, though it does not appear to be doing anything much yet. Trump says the US will now be imposing even more severe sanctions.

One can take it that the US is much more powerful than Iran, and that it has the power to assault its defence forces, military resources and population centres at will. It could, in short, lay even more waste to Iran and its economy than it already has by sanctions. But one can also take it that invasion is not on the cards - Iran would quickly become a quagmire that would make Afghanistan or Iraq seem a picnic, even after a shock and awe military campaign that put American power in most of the nation's cities.

The US faces several problems. It tends to dwell on the fact that Iran sponsors a number of "proxy" armies that make war, with Iranian arms and missiles, and training, in an array of Middle East countries. From its backing of Hamas - and possibly Islamic Jihad in Palestine, Hezbollah in Lebanon and Syria, Al Ashtar in Bahrain, the Taliban and several militia forces in Afghanistan and Pakistan, and militias and army elements in Iraq - to its sponsorship of the Yemeni rebels against Saudi Arabia, fomenting of trouble in the Gulf states, and support of the Assad regime in Syria, Iran is a major player in the Middle East. Its play is not focused only on the Iranian national interest; it affects to be the champion of the Shiite sect of Islam and the defender of Shiites everywhere. In most neighbouring countries, Shiites are a minority and believe themselves repressed by Sunni Muslims - in Iraq, Shiites outnumber Sunnis but battle to govern in a nation where, traditionally, including under Saddam Hussein, the Sunni exercised power. Iraq is also proof that empowered Shiites are as likely to govern corruptly in their own sectarian interest, persecuting their sectarian enemies, as the other way around.

So far, Iran has been very measured and deliberate in response to Trump's unilateral action in assassinating Soleimani. It sent missiles towards two Iraqi military bases, having thoughtfully signalled what it was going to do in good time to allow the bases, and their equipment, to be evacuated. The attack, however, demonstrated that Iran has ballistic missiles which are very accurate - if that had not already been obvious after a "Yemeni" attack on Saudi oil infrastructure, and, possibly, attacks of unknown origin, if with Iranian missiles, on oil tankers in the Persian Gulf. Even if the origin of such weapons is obvious, Iran generally blandly denies being the source of such attacks.

Iran, and Soleimani, have been active in directing both Shiite militias in attacks on the Iraqi government, and, in recent time, on the American embassy, as well as in trying to influence negotiations for a new Iraqi government after the previous one collapsed last month. It is not difficult to see the role of Iran as a source of weapons and training, a sanctuary, rest and recuperation centre and transit point for travelling Shiite revolutionaries, and as a nation vying to be the leading power in the Middle East. It is never quite clear whether its primary enemy is Israel or the regime governing Saudi Arabia. If the latter, Iran can say it is rather more democratic, even if very authoritarian, and rather less associated with sponsorship of international terror via Islamic State and al-Qaeda. But Saudi Arabia is our ally, and a key source of energy for the West.

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Iran's actions against America, or against its allies, could come from its proxies in neighbouring countries. But it has considerable capacity, if it wanted to, to take retaliatory action in the wider West, or perhaps, as al-Qaeda did pre-September 11, 2001, in Africa, Yemen, the Indian subcontinent or south-east Asia. That capacity cannot be underestimated. That is not a reason for allowing it to play bad international citizen - as a supposed part of the "axis of evil" - but it is a very good reason why engaging with it, in diplomacy or war, should be careful and considered. That this is not the approach being taken by Trump seems obvious in his equivocations (broadcast via Twitter) about his aims and his intentions.

But there's another problem. It is clear by now that Russia, or Vladimir Putin, completely outplayed Trump, the US and its allies (including Australia) over the fate of Syria. It may well prove to be that a byproduct of this victory has been the maintenance, in at least vestigial form, of a powerful successor to al-Qaeda and Islamic State. Putin would not be doing this because he has any time for jihadist terrorists, but because it is in his general interests to have the US, and as many of its Western allies as possible, bogged down in quagmires such as Iraq and Afghanistan - virtually unable to win, mostly afraid to be seen to lose. Oddly, Trump, who campaigned on "making America great again", and who complained that too many countries were humiliating the US, has been rather more determined to get out of some of these quagmires, in the Middle East and Hindu Kush in particular, than most of his generals, secretaries for defence and predecessors.

Russia has been giving Iran a good deal of encouragement and assistance, not least as a sort of middleman in relation to western Europe, much of which has lost confidence in both the military and diplomatic policies of Trump but wants peace in the area. So too has China, which has long been sympathetic to Iran's outlaw status, but now sees Iran as a potential partner in two-way trade in any contest for global or regional hegemony with the US. Russia and China are neighbours who stand to benefit from trade in energy and other strategic materials (not least in material unable to be choked off or blockaded in the Strait of Hormuz). In these senses, America and its allies must fear not only Iran's proxies, but the prospect of Iran being a proxy for other nations.

Australia has invested a good deal of its treasure, and not a few Australian lives, in conflict with Iran's neighbours. It has been to little effect, least of all on the strategic situation. Our involvement in Afghanistan has had no impact whatever on outcomes. Perhaps our air war against Islamic State contributed to an outcome of sorts, but that may prove to have been undone by Trump's actions in Syria. Australian military training, or direct involvement in fighting, has not helped democratise Iraq (or its army), stabilise its leadership, or reduce its grand-scale corruption and the sectarian slant of virtually all government in the country. Perhaps Australia has won some gratitude from the United States for its entirely uncritical support, but those with experience of Donald Trump would know that one can never rely on his loyalty.

Scott Morrison is now, rightly, focused on recovery and reconstruction from our bushfires. But he must also keep a weather eye on the Middle East, on India, on North Korea and on China. And, increasingly, on our great and powerful, if completely erratic and sometimes irrational, friend. Three years of Trump diplomacy suggest that America's enemies know US politics, and Trump, rather better than Trump knows or understands their politics and their leaders.