14th Amendment, Section 3.
Section 3. 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, or given aid or comfort to the enemies thereof. But Congress may by a vote of two-thirds of each House, remove such disability.
1872 Amnesty Act, repealing the 14th Amendment section 3:
"Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled (two-thirds of each house concurring therein), that all political disabilities imposed by the third section of the fourteenth article of amendments of the Constitution of the United States are hereby removed from all persons whomsoever, except Senators and Representatives of the thirty-sixth and thirty-seventh Congresses, officers in the judicial, military, and naval service of the United States, heads of departments, and foreign ministers of the United States."
The 1872 Act looks like it pretty much spells it out. But then again, these are leftist, Marxists we are dealing with. Constitution be damned.