From War Criminals Watch
President Trump declared during the Presidential campaign that he "would bring back" torture "because it works -- for intelligence gathering. He has repeated the threat upon taking office. Well, that is a position that has been extensively debunked over many years by many experts on intelligence gathering. Furthermore, in the United States presently, not only is the use of torture illegal under a variety of laws, it's also unconstitutional (an historical fact overlooked by many observers).
It happens that the use of torture by any signatory to them is prohibited by the Geneva Conventions and the UN Convention Against Torture. The United States is a party to both and both are signed and ratified U.S. international treaties. And then, under article VI of the U.S. Constitution, as treaties signed and ratified by the US government, both Conventions are part of "the supreme law of the land and [further] the judges of every state shall be bound by them." Not that the Trumpites have not already demonstrated that they clearly do not care what is, or is not, written in the Constitution, but I do think that for opponents of its use in the US, this is an important and potentially useful consideration.
However, back to the "does torture work" argument. Well, it may not, for intelligence gathering, but it surely has a bunch of other functions where it has proved to be a most effective tool -- for government repression of dissent and opposition. Consider:
The German Nazi Gestapo, the Iranian Savak under that great US ally the Shah, the Japanese fascist era Kempeitai, the Argentine and Brazilian Generals, the Pinochet Regime and the Spanish Francoists have proved over and over again that torture does have its uses. First and foremost, it is a major instrument of terror against one's own population: it is a really good repressor of dissent.
Second, it is a very good tool for extra-judicial punishment, just as long as the regime using it makes sure that its details leak out, in a totally deniable way of course, to its own citizens.
Third, it is a very useful tool for repression in militarily occupied territories. Just ask the Japanese Kempeitai that operated in Korea and Occupied China about that one.
Fourth, it is very helpful when a regime is out to change the culture of its country and to wipe out historical memory of anything that went before it came to power. Once they had restored corporate-clerical control of the country, doing so was perhaps the principal long-term goal of the Spanish Francoists. Torture was one of their stocks-in-trade.
Finally, in order to have this as a most useful instrument of national policy, one must have torturers. Until Bush/Cheney came to power, Americans didn't do such things, officially at least. So, there weren't very many, if any, trained torturers among our armed and intelligence forces. But some were trained then, and, it seems, the Trumpites want to train many more. And to train torturers, a government must torture. And so, it seems, since everyone knows that "torture doesn't work" (for intelligence gathering), training torturers must be to be able to implement one or more elements of the list above that the Trumpites have in mind, no?