Because people were convicted of seditious conspiracy.
How do you know they are Democrats?
It doesn't look that way to me. Which of the people "...Conspired to overthrow, put down, or to destroy by force the Government of the United States, or to levy war against them, or to oppose by force the authority thereof, or by force to prevent, hinder, or delay the execution of any law of the United States, or by force to seize, take, or possess any property of the United States contrary to the authority thereof, they shall each be fined under this title or imprisoned not more than twenty years, or both."?
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