Eugene McCarthy (1916–2005) was a little-known Minnesota senator until November 1967, when he challenged President Lyndon B. Johnson for the 1968 Democratic nomination for president. McCarthy’s candidacy centered on his opposition to the Vietnam War. Because Johnson was an incumbent, and McCarthy was not a nationally known figure, the challenge was not initially seen as a real threat to Johnson’s election. As public opposition to the war grew, however, McCarthy’s primary campaign gained more traction. In March 1968, Senator Robert F....