Final answer:
The assassination of Martin Luther King Jr. furthered Black doubts about American politics.
Step-by-step explanation:
The event that furthered Black doubts about American politics was 2) The assassination of Martin Luther King Jr. His assassination in 1968 was a devastating blow to the civil rights movement and left many African Americans feeling disillusioned and skeptical of the ability of American politics to bring about meaningful change. Dr. King was a prominent leader in the movement, advocating for racial equality and justice, and his death had a profound impact on the Black community.