Warning: IANALBIDLRRL*
Allow me to address myself to the first scenario. In American law, there is something referred to as the de facto officer doctrine. If a person holds an office and it is later determined that the office-holder’s actual authority suffers from some procedural defect (for example, a judge is appointed despite being statutorily ineligible for the position because she doesn’t hold a law degree), the office-holder’s acts that are done within the scope and by the apparent authority of her office are still binding. See, for example, Gates v City of Tenakee Springs, 954 P2d 1035, 1039 (Alaska 1998) (holding that an appointed pro tempore judge was a de facto judge with authority to enter findings, even though he did not meet state residency requirements for being a pro tempore judge).
“The de facto doctrine springs from the fear of the chaos that would result from multiple and repetitious suits challenging every action taken by every official whose claim to office could be open to question, and seeks to protect the public by insuring the orderly functioning of the government despite technical defects in title to office.” Ryder v United States, 515 US 177, 180 (1995) (quoting 63A Am Jur 2d, Public Officers and Employees sect 578, pp 1080-81 (1984)). Obviously, there is great appeal in invoking the de facto officer doctrine if, say, massive portions of a presidency are improper, meaning that just about everything the executive branch did in the last three years was invalid.
However, there’s two key differences here between an imposter president and cases that apply the de facto officer doctrine. First, being an imposter seems to be much more than a mere technical deficiency or procedural irregularity in appointment. It’s one thing if the President turns out, after the fact, to have been just under the age of 35 or if some of the electoral votes necessary to his election were on red paper instead of blue paper, or whatever. It’s another thing entirely to pose as someone else entirely. I think part of the rationale for the de facto officer doctrine is that the mistake was in good faith. With an imposter president, the mistake is not in good faith; indeed, to call it a “mistake” misses the mark, for what we’re dealing with is out-and-out fraud. There’s far less reason to trust an officer’s acts were reasonable if that officer achieved his office through fraud, as opposed to by means of a good faith mistake.
A second difference is the fact that the Constitution is involved rather than a statute. Article II, section 1, provides that the executive power shall be vested in a president. One president. Playing switcheroo with the person wearing the President hat seems to be playing fast and loose with the concept of a single executive officer. Consider Ryder v United States, 515 US 177, 180-84 (1995) (refusing to apply the de facto officer doctrine to the authority of a judge when there has been a trespass upon the constitutional power of appointment, rather than merely a misapplication of the statute providing for the assignment of already appointed judges).
Thus, it would seem that the imposter president is not a de facto officer. Thus, every action the imposter president took is invalid for want of authority to do it. This would be catastrophic, as it would appear that the acts of all executive officers nominated by the imposter president would also be invalid. This is why scenario (2) would be less dangerous. At least the imposter Clinton already had executive officers in place. They’re actions would be valid, as they were duly appointed.
*I Am Not A Lawyer But I Do Look Remarkably Rat-Like