The era of Congressional ("Radical") Reconstruction can be seen as a failure because A) it prevented Southern states from holding elections.
B) it punished all people in the Southern states equally.
C) it resulted in the severing of ties with former European allies.
D) it did not adequately protect former slaves from having their rights violated.

D)it did not adequately protect former slaves from having their rights violated.

Explanation:

The era of Radical Reconstruction can be seen as a failure because (D) it did not adequately protect former slaves from having their rights violated. The radical reconstruction commenced in 1867, and ended in 1877 with the fact that racial inequality was rife.

answer; (a) he was a u.s senator for 38 years;

if i am correct the answer is going to be a) the federal program of reconstruction ended.