No standing.
Statute of Limitations.
No one cares any more.
No reasonable prosecutor would bring the case to trial.
No controlling legal authority.
We lost the files.
The files have been contaminated.
The list of reasons why so-and-so is untouchable is very long. Bottomline is: “It’s a big club, and you ain’t in it.”
There's no statute of limitations on murder. Barack Obama was ineligible to serve as President of the United States and every individual killed in drone strikes and such is one count of murder. He had no authority to order the attacks.
Don’t forget the Hillary line: What difference does it make?