Nonetheless, Mueller emphasized that “the investigation of a sitting president...is important to preserve evidence while memories are fresh and documents available.” Now, what does that mean? There is obviously only one reason to investigate while the trail is still hot. Once Trump leaves office, and if he does so within the five-year statute of limitations for obstruction of justice, he can then be prosecuted. Indeed, the Mueller report reflects that his office developed evidence showing that Trump may well be guilty of eight instances of obstruction justice for a wide variety of obstructive conduct.