Final answer:
Under President Lincoln's Reconstruction plan, individuals who had engaged in insurrection or rebellion, or supported enemies of the United States, were not permitted to take the loyalty oath and hold public office unless their disqualification was removed by a two-thirds vote of Congress.
Step-by-step explanation:
Under President Lincoln's plan for Reconstruction, certain individuals were not permitted to take the oath of loyalty and become citizens again. Specifically, those who had engaged in insurrection or rebellion against the United States, or provided aid and comfort to its enemies, were barred from being a Senator or Representative in Congress, elector of President and Vice-President, or holding any office under the United States or any State. This exclusion applied to any person who had previously taken an oath to support the U.S. Constitution as a member of Congress, officer of the United States, member of any State legislature, or as an executive or judicial officer of any State. However, Congress had the authority to remove such disqualification with a two-thirds vote of each House, according to Section 3 of the 14th Amendment.