Simply put, the 2A is to keep the government in check, not the people....I wrote it off the cuff. If I were to refine it -
The Second Amendment is for when the system fails. It applies to ALL organs of the state; whether they make laws, wear badges, or carry gavels.
I might tweak it some more.
Legislative, Executive, and Judicial - the 2nd Amendment holds all accountable to the people.
Legislators, Cops, Judges - the Second Amendment holds all in check.
Still too long for a bumper sticker.