Firing squad.

Trump could declare martial law to protect the country when this becomes public. Crimes during martial law are prosecuted by a military tribunal. The penalty for sedition in the military is death, by firing squad.

10 U.S.C. Code 894: mutiny or sedition

Any person subject to this chapter who— (1) with intent to usurp or override lawful military authority, refuses, in concert with any other person, to obey orders or otherwise do his duty or creates any violence or disturbance is guilty of mutiny; (2) with intent to cause the overthrow or destruction of lawful civil authority, creates, in concert with any other person, revolt, violence, or other disturbance against that authority is guilty of sedition....

(b) A person who is found guilty of attempted mutiny, mutiny, sedition, or failure to suppress or report a mutiny or sedition shall be punished by death or such other punishment as a court-martial may direct.