derived from a specific historical event (video documentation), when the commander in chief addressed an active-duty armed forces division in a militarized zone. with careful diction, the president punctuated his statement : "and you will ... complete your --- "
the pronunciation of "mission," elicited from the division--in all but perfect unison-- a slow crescendo, a roar, something like "rah" at its peak.
the noteworthy aspect is both aural and visual. half a beat after the word was spoken (an apparent, if experimental, verbal prompt) the division members slowly raised their heads and emitted--some tentative, at first, some strong, then as a chorus--the crescendo-roar. it gave the distinct impression of hypnosis on a mass scale.
the phrase then, not only denotes the incident described, but also the feelings elicited by it. more generally, it denotes the event (real or hypothetical), of grand-scale, schematic influence of human behavior/performance. (at least, and specifically in this case, to the degree of verbal prompting.) it might also be used as an epithet.
more generally: any time a large group, say ten thousand or more, responds to a verbal prompt in a manner that suggests a subliminally embedded cue, called out by the speaker. the cue word is not important, may be obvious, even anticipated; rather, it is the nature of the response. timed, rhythmic, spontaneous, choral, lacking in self awareness.
those from whom the response is elicited--depending on the individual, situational variables and controls--may identify it as an instance of manipulation, extrapolate and assess the implications.
if conditions allow for a phenomenological analysis of a perceived violation (that takes precedence over a given emotional response such as outrage), a reverse "challenge" (hypnotic motivation institute, glossary of terms: hypnosis.edu/glossary/c) might emerge.
consider for instance, the prose inked by radiohead on their 2001 release, AMNESIAC (copyright EMI LTD.) : "come on. come on if you think. you can take us ... all on. holy roman empire. you and whose army? you and your cronies..."
one might dismiss such an event as accidental.(a paltry dismissal.)or, with a casual reference to the ubiquity of nuero-linguistic programming.
but key here is the scale. the context. the super-spooky.
ergo, mission creep.
slows down the process and causes things to creep along