It strikes me that 44 of 45 presidential terms have been filled, without immunity. I'm sure Nixon would have invoked it in his case, if such a thing were actually real. Why is Trump suddenly arguing about it?
Should the SCOTUS rule in Trump's favour, I have no doubt that a future SCOTUS will reverse such a travesty of justice. It may take time, but it will happen.
Imagine this coming around in a turn ... perhaps a sloe cycle like that ridden by ET? Then in some Semitic tongues ET is a tree ... and there folk in the OT were hung up by their hairs ... these myths are complex so as to hide the virtue ... and things we didn't wish to know about the questionable self ... there it goes over the trees and greens ... Vertis Ghost?

