I've always seen malleable in the figurative sense, "capable of being adapted by outside influences," which comes from the 1610s. As in the inveterate huckster, the presidential candidate, who is able to gather more than enough support from a weary, malleable electorate believing change will truly occur if they cast their vote for the person who tells them what they want to hear.

Generations of Drill Instructors have been yelling at recruits to see if they are malleable enough and packing the gear to be a Marine. If they can't take getting yelled at, getting shot it is out of the question. DI's have to be hard and want you to quit because they don't want to take quitters into combat. They have to be special people. They can't be sadists, although to watch the process, you might think so. Neither can they be pushovers. Many recruits hate their DI in boot camp. Once they pass and go from recruit to Marine, when their DI tells the recruit that he is proud of him, it is one of the finest moments of their life.