Please explain what you are talking about? If Joe Biden is allowed to be inaugurated, there is no authoritative agency that can do a thing to him even "if the evidence clearly shows fraud." The President is the head of the Executive Branch. All police agencies report to him. Congress is the only check and balance even "if the evidence clearly shows fraud." Impeachment is the only recourse.
If a cadre of Federal Marshalls walked into the Oval Office and said, Mister President, we have a warrant for your arrest. Joe Biden would tear it up and tell the Marshalls they are fired and charges will be brought against them. End of story.
I think that Trump is president until noon on the 20th....there can not be two presidents...one steps down the other takes over....