Here is a pretty decent piece on the ruling by three reputable attorneys...
Here is a pretty good summary of the three prongs of the Robert's court's immunity applications:
"Writing for a 6-3 majority that split on party lines, Chief Justice John Roberts established a three-level immunity test: (1) absolute immunity when the president is exercising “his core constitutional powers,” (2) “presumptive immunity from prosecution for his official acts” that are not core to presidential duties (such as exercising powers given to him by Congress) and (3) “no immunity for his unofficial acts."
The issue is going to be about the definition of what an "official act" will be. Of course, some are easy, and others aren't.
