Who's to say that maintaining the dignity of the office of President is not in the interest of the US? She is impugning his reputation therefore making him look weak which could embolden our enemies. She must disappear for the good of all Americans.
It's not hard to justify just about anything as an official act in the interest of the US.
Not really. Exercise of a Presidential power, no matter the reason, is immune from prosecution. If it's legal to drop a bomb on ISIS it's legal to drop a bomb on a pornstar.
A lot of people are reading this wrong. What is likely going to happen is that the district court will say that a grand Jury can decide if something is an official act. That might be challenged again but I'd wager that's the next stop in this saga.
But don’t forget that official government records and any inquiries as to the motives of the president will not be admissible as evidence in any such case.