It says anyone who had previously taken an oath to support the constitution, which is pretty much any federal government employee, including civilian workers, members of the military, members of Congress, members of the Executive Branch (including the president), members of the Judicial Branch, etc.

Emphasis mine. Below is the text of section 3 of the 14th amendment. It disqualifies anyone who has previously taken an oath to support the constitution who engages in insurrection or rebellion against the constitution.

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.