Exile and execution should always be available for seditionists and traitors in a time of war. I'm sure there are plenty of people that would LIKE to become American citizens and proud of it.
Without a declaration of war, traitors go unpunished. Sedition laws should always be avoided, or if necessary, made to apply most harshly to elected officials and government employees, both of whom are in a position to cause damage by their speech. Sedition laws are too easily abused by people in government who are prone to abuse power. This is why those laws are repealed after a war ends, because they conflict with the right of free political speech.
A declaration of war is the dividing line between treason and free speech. The President should press for a declaration of war to observe Constitutional rule and to bring treason into the jurisdiction of the military courts. Otherwise, prosecution is nearly impossible in many cases and improper in every case.