The primary reason Republicans in Congress felt that the Fourteenth Amendment was necessary was:
2. They worried that President Johnson would not enforce the Civil Rights Act.
After the Civil War, there was significant concern about the protection of civil rights for African Americans, particularly in the former Confederate states. The Civil Rights Act of 1866 was a vital piece of legislation, but many Republicans were apprehensive that President Andrew Johnson, who had a lenient approach towards the South and was not fully committed to enforcing civil rights protections, would not uphold the laws passed by Congress. The Fourteenth Amendment was aimed at solidifying these rights and providing a constitutional basis that would ensure their enforcement, thus addressing concerns over both state compliance and presidential enforcement.