Yesterday a sitting member of Congress, who is pretty much the face of the Republican Party, tweeted her support for the doctrine of secession.
The United States Supreme Court has rather clearly addressed this sort of thing.
"The doctrine of secession is a doctrine of treason." -U.S. Supreme Court, White v. Hart (1871).
For further context, this person also suggested “a bullet to the head” as a quick means of removing Nancy Pelosi. The GQP is now openly pushing a doctrine of treason.