4.) PG here, Enter John Adams, a barrister with a sense of humour. He showed up the conundrum in clear language:

The public good, the salus populi is the professed end of all government, the most despotic, as well as the most free.
What Adams & others did when they were writing the basics for the US state was essentially to rework not only the words but the context of Cicero’s original.
The maxim is no longer sage advice to a potential ruler but now a bold assertion that the public good is determined from the perspective of a public who is the ruler.
The first words uttered by Charles I at his trial were the majestic Hobbesian “I would know by what power I am called hither.” The Puritans were unable to sustain their answer, but their successors across the Atlantic eventually provided “We the people.” So there.