No person shall be a Senator or Representative in Congress, or elector of President and Vice-President, or hold any office, civil or military, under the United States, or under any State, who, having previously taken an oath, as a member of Congress, or as an officer of the United States, or as a member of any State legislature, or as an executive or judicial officer of any State, to support the Constitution of the United States, shall have engaged in insurrection or rebellion against the same...
He took an oath as a member of the military, he also took part in insurrection.
The crimes charged in the indictment involve active participation in an insurrection attempting to violently overthrow the United States Government. By Chansley’s own admissions to the FBI and news media, the insurrection is still in progress and he intends to continue participating.