While I was searching about what are the restrictions on former US Presidents concerning the United States' own security and its classified information. I found nothing more than a Wikipedia page Former Presidents Act . But that page is not much use for what I am interested in.
I would especially like to know: can an ex-president of the United States settle in another country with which the current US relations are not very good or tense, or which is/was hostile towards the US, if he wishes to?
Sure, same as any other citizen.
It would seem unlikey that a "hostile" country would grant a visa, but if they did, then there is nothing in law or the constitution to prevent a former President from leaving the USA.
It would raise some eyebrows politically. The CIA would be quite concerned. If it was thought the ex-President was giving state secrets, then I wouldn't be too surprised if there was some kind of CIA black-ops. But the USA doesn't have exit visas. It allows citizens and former citizens to take up residence abroad. There are no special laws for the President.
The President might lose many of the benefits, such as pension or secret service protection.
It has never happened. No President has retired even to a friendly country, though there has been talk of Trump moving to Scotland to spend more time with his golf clubs. (Is Scotland hostile to the USA? It is certainly hostile to Trump)
