Rep. Bennie Thompson, D-Miss., and the NAACP are suing former President Donald Trump and his longtime ally Rudy Giuliani for allegedly conspiring with a pair of hate groups to storm the U.S. Capitol and block the Electoral College count in January. And they’re using a 150-year-old law as the basis of the suit.

Thompson and the NAACP, the nation’s oldest civil rights organization, allege in the suit, obtained by NBC News, that Trump, Giuliani, the Proud Boys and the Oath Keepers used “intimidation, harassment, and threats,” to stop the vote count and caused the Jan. 6 Capitol riot in the process. This, they said, violated the Ku Klux Klan Act of 1871.

“I guess it tells you something when you can use a Ku Klux Klan law from the 1870s,” said Brian Levin, director of the Center for the Study of Hate and Extremism at California State University. “It’s part of a series of laws enacted after the Civil War. Everything old is, unfortunately, new again.”