It’s against the law to conspire to overthrow the government of the United States. It’s called treason.
We prove the point, arrest the traitors and put them on trial.
18 U.S. Code 2384 - Seditious conspiracy
If two or more persons in any State or Territory, or in any place subject to the jurisdiction of the United States, conspire 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.