Posse Comitatus, definitions

By the time I got to the PC thread it was already closed. Read a few pages, but never found the actual topic being discussed.

Posse Comitatus has 2 meanings as I understand it, and I would love input from others.

The Posse Comitatus Act was passed in the US after the Civil War, and was intended to restrict US Army troops from enforcing civilian laws. Though the statute is still on the books I think, it was effectively nullified during the Reagan administration and its version of the drug war.

Then under Common Law heritage, Posse Comitatus was a principle that obligated every citizen to assist the local Sheriff if requested. To join the Sheriff's posse, supposedly to capture some felon or the other.

Any thoughts?