However, a small group of Progressive Labor Party and SDS protestors activists placed themselves at the head of the march and, when they reached the hotel, staged a sit-down. Efforts by march monitors to keep the main body of the marchers moving were only partially successful. Hundreds of LAPD officers were massed at the hotel and when the march slowed an order was given to disperse the crowd. The Riot Act was read and 51 protestors arrested.[241][242] This was one of the first massive war protests in the United States, and the first in Los Angeles. Ending in a clash with riot police, it set a pattern for the massive protests which followed.[243] Due to the size and violence of this event, Johnson attempted no further public speeches in venues outside military bases.[243][242]
In October, with the ever-increasing public protests against the war, Johnson engaged the FBI and the CIA to investigate, monitor and undermine anti-war activists.[244] In mid-October, there was a demonstration of 100,000 at the Pentagon; Johnson and Rusk were convinced that foreign communist sources were behind the demonstration, which was refuted by CIA findings.