...that doesn't mean that the law is either enforceable or Constitutional, and this law has never even been tested in this manner. (The Clinton case was a lawsuit against NARA, not Clinton.) If the PRA were ever adjudicated in such a way that a president actually were prosecuted on it, then it would be tossed as unconstitutional for multiple reasons, including separation of powers and vagueness.

The reason that the PRA is a defense against the fraudulent espionage charges is because the law states that the president has SOLE responsibility for categorizing his docs. It lays out some vague ground rules for doing so, but it is toothless because the president still makes the call. If he categorizes a report on nuclear submarines as personal, then that may be unethical, but it's not illegal or unconstitutional because he has SOLE authority to do that. Which means it is beyond review. Which means he can't be prosecuted for it. A NARA bureaucrat doesn't trump that authority, and neither can another branch of government (i.e., the judiciary branch).

The espionage charges against Trump will ultimately fall apart based on numerous fatal flaws, and the PRA is one of them.