Your use of this act sent me scrambling. Google sent me to www.dojdov.net/posse. I also consulted my copy of Gunsmoke Over Lincoln County, by Phillip J Rasch. You will already have been well versed in this act.
I had jumped in feet first though, and did not do my homework. True in 1878, the Posse Comitatus act was created. It reminded me that primarily, it forbade the use of the US military in police matters. Of course it was applicable in the internal struggles between US civilians.
I note, in my own defense, that in the Lincoln County War, the military mostly turned away from the violence of the two factions. These were the McSween- Dolan factions. The military sent all kinds of information on these factions, to the various civilian bodies in Washington and New Mexico. No problem there. I guess somebody should lose their jobs over this one. Security is paramount to shilly shallying.
Yes, and the original version had provisions for exceptions. These provisions, however, were in keeping with the civilian control of the military, in that it was only within the power of Congress to authorize and the Sec'y of Defense to regulate exceptions. But once again, without printing out and parsing an up to date version of the act and going over the language, line-by-line with a ruler as I do contracts, do I find anywhere that it is against the law for the US Army to inform the FBI that known terrorists are within the jurisdiction of domestic law enforcement.
This business of a "wall" reminds me of how the ACLU protected American born Soviet agents from being prosecuted at home for passing on secrets abroad. A practice that has been a tradition of the left since before Ethel and Julius Rosenberg. And, FWIW, nuclear weapons are excluded from any protection of the Posse Comitatus Act, (18 U.S.C. 831 (e). If a terrorist cell can be considered to place the public in the same peril as a WMD, then what is the problem with the sharing of the activities of foreign nationals from terrorist states within the borders of the US.
In the end, it appears that 9-11 was the caused by Muslim terrorists and permitted by government lawyers.
it forbade the use of the US military in police matters.
And the long-timers here at FR can cite chapter and verse regarding Posse Comitatus issues in the early Clinton administration - in one word - Waco.