They're only pre-approved for explicit constitutional duties, but they're presumed immune for all others and their reasoning can't be questioned. "I believed they were an imminent national security threat and took the hard choice." It's like "I feared for my life" for gun nuts, but you can apply it to nearly anything because the president has expansive emergency responsibilities and the only way to prove he wasn't actually taking an action "officially" would be using his private communications, but any communications with "advisors" are precluded from being used.
And anything that makes it through that gauntlet to the Supreme Court rather than being dismissed earlier will be decided on ideological grounds.