Consider the following two hypothetical* situations:

a) Government agent hacks into private email account without a warrant, discovers that citizen is seeking bomb-making materials, initiates detention of citizen

b) Private citizen hacks into presidential candidate email account, discovers candidate is in regular communication with far-right groups on how best to coordinate strategy, publicizes communication to discredit candidate

Which of these actions should be illegal, and why?

* Note, I am not saying that the current situation under discussion is exactly like b), even though there are superficial similarities.