The original sentence-
Many powerful leaders throughout history, such as President Nixon
during the Watergate debacle,
had become victimized by his own paranoia.
Such as President Nixon
during the Watergate debacle - (noun phrase) is fine to mention an example. President Nixon is a noun with modifier "during the Watergate debacle" .
The choices -
(A) Many powerful leaders throughout history, such as President Nixon during the Watergate debacle,
had become victimized by his own paranoia.
HAD - Past perfect tense requires reference of something in simple past. This is incorrect.(B) Many powerful leaders throughout history, such as President Nixon during the Watergate debacle, have become victims of their own paranoia.
Correct.(C) Many powerful leaders throughout history, such as President Nixon during the Watergate debacle, has become victimized by his own paranoia.
Subject verb disagreement. Many powerful leaders - plural subject can't have HAS. (D) Throughout history,
many a powerful leader, such as President Nixon during the Watergate debacle,
have by his or her own paranoia become a victim.
S-V agreement issue.(E) Throughout history, a few powerful leader, such as President Nixon during the Watergate debacle, had by his or her own paranoia become a victim.
HAD - Past perfect tense requires reference of something in simple past. This is incorrect.IMO
B