A preemptive, blanket pardon for the past ten years Should be amusing watching Jean-Pierre try to defend that.
No charge is required.
Today's pardon covers any act of treason [federal crime] committed during the time specified. He would have to be charged by a state attorney somewhere.
Read the pardon. It covers any federal crime Hunter committed in those ten years, and there is nothing prohibiting a pardon for treason.
The sauce is the Constitution. If a pardon could not be given for acts of treason, it would be specified in the Constitution.