1968

"A faction led by Eugene McCarthy, a committed anti-war candidate, began to challenge the long-held assumption that the United States should remain in the war. As the debate intensified, fights broke out on the convention floor, and delegates and reporters were beaten and knocked to the ground. Eventually, the delegates on the side of the status quo, championed by then-Vice President Hubert Humphrey, won out, but the events of the convention had seriously weakened the party, which went on to lose the following election.

Meanwhile, on the streets of Chicago, several thousand anti-war protesters gathered to show their support for McCarthy and the U.S. withdrawal of troops from Vietnam. Chicago Mayor Richard Daley deployed 12,000 police officers and called in another 15,000 state and federal officers to contain the protesters. The situation then rapidly spiraled out of control, with the policemen severely beating and gassing the demonstrators, as well as newsmen and doctors who had come to help.

The ensuing riot, known as the “Battle of Michigan Avenue,” was caught on television, and sparked a large-scale change in American society. For the first time, many Americans came out in virulent opposition to the Vietnam War, which they had begun to feel was pointless and wrongheaded. No longer would people give the national government unrestrained power to pursue its Cold War policies at the expense of the safety of U.S. citizens."
http://www.history.com/this-day-in-history/protests-at-democratic-national-convention-in-chicago