In early January 1968, Secretary of Defense Robert McNamara said the war would be winding down, claiming that the North Vietnamese were losing their will to fight. But, shortly thereafter, they launched the Tet Offensive, in which they and Communist Vietcong forces undertook simultaneous attacks on all government strongholds across South Vietnam. Though the uprising ended in a U.S. military victory, the scale of the Tet offensive led many Americans to question whether the war could be "won", or was worth the costs to the US. In addition, voters began to mistrust the government's assessment and reporting of the war effort. The Pentagon called for sending several hundred thousand more soldiers to Vietnam. Johnson's approval ratings fell below 35%. The Secret Service refused to let the president visit American colleges and universities, and prevented him from appearing at the 1968 Democratic National Convention in Chicago, Illinois, because it could not guarantee his safety.