"....and where would the records be for his swearing in?"
No one has the slightest idea....Least of all the Supreme who swore him in.
...if he is not a citizen at all, how can he be charged with treason against a country he is not a citizen of?"
Right...you got me there. I should have used "terrorist", "saboteur", or ..........Wait a minute...
The Constitution of the United States, Art. III, defines treason against the United States to consist only in levying war against them, or in adhering to their enemies, giving them aid or comfort. This offence is punished with death. By the same article of the Constitution, no person shall be convicted of treason, unless on the testimony of two witnesses to the same overt act, or on confession in open court.
Nothing about being a citizen in this! I may be saved...{:-)
On further review (of your excellent question): Leave in "treason" and additionally include "terrorist" and "saboteur".
I guess a lot will depend on how big the turnout will be at the 9/12 March.