The conviction of Henry “Enrique” Tarrio, former leader of the Proud Boys, for seditious conspiracy advances the cause of justice for the Jan. 6 insurrection. However, as the mall shooting in Texas makes clear, the threat posed by domestic extremists continues. On Thursday, May 4, a jury in Washington, D.C., found Tarrio and two other others guilty of seditious conspiracy for planning the attack on the U.S. Capitol. They acquitted a fourth defendant but found him guilty of other crimes related to Jan. 6. The seditious conspiracy statute, which dates to the Civil War era, makes it a federal crime...