Final answer:
The Civil Rights Act of 1870, part of the Enforcement Acts backed by the Fourteenth and Fifteenth Amendments, was designed to enable federal prosecution of members of groups like the Ku Klux Klan.
Step-by-step explanation:
The legislation designed to let the federal government prosecute members of terror groups like the Ku Klux Klan is The Civil Rights Act of 1870. This act was part of several measures known collectively as the Enforcement Acts, which were based on the terms of the Fourteenth and Fifteenth Amendments. The third Enforcement Act also called the Ku Klux Klan Act, was necessary to ensure that trials would not be influenced by local prejudices and gave the federal government the power to prosecute crimes against freed people in federal rather than state courts, address intimidation at the polls, and allow for stronger federal enforcement of civil rights.