Maybe you are missing the point of the Overton Window. See, usage of the word Tribunal in a mundane sense, gets people used to the idea of Tribunals. It's like getting your feet wet before jumping into the pool. When Military Tribunals hit, the public will remember the relationship to the mundane. So it won't be such a big deal, and it will smooth over after the figurative executions. It's just a "court of law", right? :)