Sometimes thought of as the opposite of a Texas Sharpshooter, “moving the goalposts” is a way of changing the criteria for proving the validity of an argument, often after they have already been met. As Rationalwiki points out that certain movements seem prone to doing it more than others, but I’ve seen this fallacy used by a lot of people. Listserve debates are a common place for this as a rhetorical tactic, although listserve debates are generally a great source of examples of every form of logical fallacy.