WASHINGTON — In the first few months of Donald J. Trump’s presidency, if recent history is any guide, intelligence officials will meet to discuss a terrorism suspect living abroad. This suspect might become the next target for the nation’s not-so-secret drone force. Or maybe, Mr. Trump’s advisers could decide, he is worth trying to capture.

Under President Obama, security officials have followed a familiar script once they have taken someone into custody. They ask an allied country to conduct the interrogation, or instead question the suspect aboard an American warship using military interrogation techniques, then turn him over to the Justice Department for prosecution in a civilian court inside the United States.

Mr. Trump campaigned on a promise to bring back waterboarding, a banned method previously used by C.I.A. interrogators, and allow unspecified practices he called “a hell of a lot worse.” The president-elect said in an interview last week that he had heard compelling arguments that torture was not effective, though it is not clear whether he intends to retreat from his position.

If he moves ahead to fulfill his campaign pledge, it will not be easy. Federal law, international pressure and resistance from inside the C.I.A. stand in his way. Even if he overcomes those obstacles, the toll of America’s agonizing treatment of captives has left a legacy of harm that will make it harder for Trump administration lawyers to justify resuming use of the tactics.