It is easy – and because it is easy it constitutes also shameful demagoguery – to pick up votes by acting tough in the wake of tragedies like the terrorist attack in Brussels.

Donald Trump must know that "acting tough" is just that: acting. His suggestion that the terrorist attack might have been thwarted if Salah Abdeslam was tortured is at best wild speculation. Abdeslam had been detained only days before and, being the dangerous and experienced criminal that he is, he very likely would have sent interrogators and law enforcement officials on wild goose chases while pretending to tell them what they wanted to hear. Not only would the terrorist attack happen anyway, the vital resources needed to prevent future attacks would have been squandered.

News reports claim that Abdeslam is cooperating with law enforcement. It is too early to tell whether this is happening without coercion or even if it is true that he is cooperating at all; we will know when that information can be corroborated through objective, neutral sources.

But if it is true, it more than likely is happening because he is being interrogated by professional investigators who know how to elicit intelligence and evidence without violating cardinal principles of fair trial and respect for human dignity. Experienced professionals also know what works in these cases, and what works is certainly not torture, as decent law enforcement officers, in the US and in many civilized countries, will readily tell Mr Trump.

"If it was up to me and if we changed the laws and have the laws, waterboarding would be fine," said Trump.

He can say that waterboarding is a "minimal form" of torture. We know by now that he can and will say anything. But on this matter it is clear he has never been waterboarded himself, even for a few seconds. That a technique that consists in generating a fear of asphyxiation by drowning could be considered anything other than torture is baffling.

Donald Trump slams British Muslims during GMB interview about Brussels attacks with Piers Morgan IBTimes UK

That is why the "torture memos" were withdrawn by the George W Bush Administration as soon as they were leaked to the public. Waterboarding is torture, as would be anything Trump has in mind as "a hell of a lot worse than waterboarding."

Torture is absolutely prohibited because it is immoral, and promoting the use of torture is illegal and immoral as well. It is forbidden not only as a matter of international law, but also as the domestic law of every country and the constitutional law of the United States.

The prohibition is not the creation of "eggheads" that don't know how the real world operates. Like Abraham Lincoln, who in the middle of the war between the States enacted the Lieber Code to regulate the conduct of the armed forces in combat.

This ban has developed over centuries from the experience of law enforcement and military leaders who know exactly why it should be banned: because it is immoral, and because it is counter-productive on many levels. This prohibition is an achievement of humankind.

Juan E Méndez is the UN Special Rapporteur on Torture