In the months leading up to Dr. Martin Luther King’s assassination in 1968, his disapproval rating was 75%; that was among White and Black Americans.
In the months leading up to Malcom X’s assassination in 1965, the Nation of Islam threatened his life, and eventually had a hand in his killing.
For Dr. King his stance against the Vietnam war was a hugely unpopular one. His growing voice against the economic disparities rather than racial ones was also not a popular stance to take. Also, many radicals in the civil rights movement grew more and more impatient with his teachings and method of nonviolence.