The growing scale and savagery of the war in Vietnam created growing dissent back in the United States. Johnson was politically weakened by the anti-war movement.

In 1968, communist forces launched wide-scale attacks throughout South Vietnam to coincide with Tet, the Vietnamese new year. The communists hoped to spark a general uprising across the country, a mission that ultimately failed. But the strength of the offensive came as a shock to the American public and Johnson.

He offered to begin peace talks with the North Vietnamese -- and announced he would not run for another term in office.

In May 1968, peace talks began in Paris but soon deadlocked. Richard Nixon, who had begun his campaign for the presidency, called for an "honorable" end to U.S. military involvement in Vietnam. But his campaign aides were secretly urging South Vietnamese officials to not strike a peace deal until after the election.