It is difficult to gather useful information through torture, and attempting to do so can have far-reaching consequences

Does torture work? Donald Trump believes so. If constant use over thousands of years of human history indicates efficacy then he might seem to be right.

The use of coercion, including the inflicting of pain and extreme discomfort, to extract information has been attractive to those charged with protecting the public – as well as to criminals, psychopaths, warlords, dictators and sadists, for as long as any have existed.

The Egyptians, Greeks and Romans all used torture. The adjective “medieval” prompts a mental image – in part due to the film Pulp Fiction – of barbarous implements used to force people to divulge something they would rather keep silent about.

So the temptations are clear, and reinforced by dozens of films, TV series and books in which crucial facts are beaten out of prisoners by tough but righteous mavericks with no time for liberal objections.

The reality is rather more complicated, as even toughened intelligence professionals will admit. The first problem is that it is extremely difficult to gather useful and actionable information from an individual under torture. Anything said under duress is inherently unreliable. Even tactically, let alone morally, this is a problem.

If someone is screaming that a bomb will go off in a particular location, do you act on that information when they might be simply telling you something, anything, to make the pain stop? Act on the lead and you could miss the real explosion, which the subject of the torture might not know anything about, or waste valuable resources and time.

“You can always make someone talk … The problem is what they say,” one of Saddam Hussein’s former torturers said when he was interviewed in a Kurdish jail in 2003.

Courts recognise this and will not admit evidence obtained in such circumstances. This may not bother the interrogators, but it should bother any of their superiors – right up to the commander-in-chief – who hopes to secure an eventual conviction.

The only reliable way to extract information, as experienced interrogators such as Ali Soufan, one of the lead FBI investigators after 9/11, have repeatedly said, is to build a rapport with a subject. Soufan did this with Abu Zubaydah, a senior al-Qaida logistician, and extracted useful information such as the name of the operational mastermind of the 9/11 plot, Khalid Sheikh Mohammed.

Soufan’s approach was deemed too soft by the CIA, which replaced him with contractors who introduced various violent tactics including waterboarding. Nothing they obtained proved that Soufan’s approach was the wrong one.

Indeed, the waterboarding of a former California gang member turned junior militant called José Padilla in 2002 resulted in a scare about a “dirty bomb” targeting the US. This supposed conspiracy was eventually found to have been based on an internet article Padilla once read, and was utterly insubstantial.

The argument over whether torture works peaked with the killing of Osama bin Laden in 2011. The intelligence that permitted this successful operation originated from multiple streams over more than a decade, and from the work of thousands of analysts. Much of this information was gathered electronically, much came from partners (including some that use torture systematically), some came from so-called open sources, and much came from people convinced without physical coercion to give up information.

But there is no conclusive evidence that the torture of al-Qaida suspects such as Khalid Sheikh Mohammed, who was waterboarded dozens of times, was the key element that allowed Bin Laden to be located and killed. The CIA claimed it was. A Senate committee that investigated those claims said it was not.

“Within days of the raid on [Bin Laden’s] compound, CIA officials represented that CIA detainees provided the ‘tipoff’ information on Abu Ahmad al-Kuwaiti [a crucial courier]. A review of CIA records found that the initial intelligence obtained, as well as the information the CIA identified as the most critical – or the most valuable – on Abu Ahmad al-Kuwaiti, was not related to the use of the CIA’s enhanced interrogation techniques,” the committee’s report said.

All these issues, so blithely ignored by the proponents of torture, are important. Because torture has immense costs. These are significant enough to outweigh any tactical gain, should there actually be any.

Firstly, there is the cost to the torturers, however little pity we feel for them. A country that tortures has to deal with scores, hundreds, even thousands of brutalised, traumatised individuals afterwards.

Then there are the consequences for the institutions concerned – the CIA, the military, whoever. The use of torture is never uncontroversial, dividing colleagues, demoralising comrades in arms, and stripping much-needed legitimacy in the eyes of a wary and sceptical public from those supposedly fighting on their behalf.

There are also consequences for nations, which may suffer massive reputational – “soft power” – damage.

There are multiple historical examples of this. The administration of George W Bush, which allowed systematic torture in CIA detention centres and elsewhere from 2002-08, was influenced by lessons drawn from the Gillo Pontecorvo film The Battle of Algiers, in which French troops fighting Islamists and nationalists in the north African city in 1956 use torture to extract information that is used to significant tactical effect. effect. The Pentagon organised a viewing in 2003.

Senior US defence officials and soldiers watched the film again several years later. The “war on terror” was going badly, with chaos in Iraq and continued Islamist attacks around the world. This time they took away a different lesson. The French won a short-term victory that partially depended on torture, but, in the long run, they suffered a devastating defeat in Algeria within six years.

Their systematic use of torture played a significant part in their failure to keep the colony. It traumatised tens of thousands of service personnel, undermined domestic support for the army – and thus the war – radicalised and motivated the enemy, tarnished the reputation of France as a democracy around the world, and had deeply unhealthy consequences for France as a nation for decades afterwards. It poisoned relations with the newly free Algeria and continues to harm French diplomatic relations across the region and beyond.

The US has paid many of these costs over the past decade, and is still paying them. Trump may believe “torture works”. It is unlikely he has the slightest idea of how expensive that thinking may prove to be.