Do you think this hypothetical political scenario can apply in real life?

Yeah. The problem with a treaty like this is no one would ever enter it, the least of which the US. There is barely any real international law, in reality. It is all about power.

That already exists. It is called the International Criminal Court, and as you would expect, the colonies along with the other great offenders, have refused to recognise it.
They have even openly threatened violent actions against the court and its members, should they ever dare to do anything against them.
That is the thing with openly imperialist countries. They are fine with prosecuting the crimes of others, but if there is the possibility of getting prosecuted themselves, they will block any such attempt.

What country do you actually believe would EVER sign such a treaty? And treaty or not, there isn’t a chance in hell of the United States surrendering ANYONE, let alone a former President to undergo Chilean justice. The United States could, would and has already thumbed its nose at such a request because there’s next to nothing Chile can manage in leverage against the United States.

In your example, I can’t see Chile ever being able to do a fair trial, because the whole premise of their prosecution is political.

@elbanditoroso: But suppose that, under this treaty, whatever person of whatever state can be subjected to trials for crimes against humanity on trumped-up charges by another trumped-up state.