Nice article: Posse Comitatus Act only applies to the Navy or Marine Corps by regulation ... and the Coasties are out of the picture, since they enforce the law under their DOT role.
If you read and believe James Bamford's book, "Body of Secrets" the Posse Comitatus Act didn't seem to bother some folks in the early 1960s from engaging in what seemed to be the plot for Frankenheimer's 1964 movie "Seven Days in May."
More recently, an essay written by an Air Force officer --got him in some hot water (so much for the First Amendment) -- surfaces the tension because the military is perceived as capable of doing everything (sounds like the premise for federalization of airport security). If you can find it, read "The Origins of the Coup of 2012." (US Army War College, Parameters, Winter 1992/93)
Cheers,
Brian