Johnson hoped to pressure the North Vietnamese and their Viet Cong allies to give up, while at the same time avoid drawing China or the Soviet Union into the fighting. He had sent 550,000 U.S. troops to South Vietnam by 1967, a vast increase from the 16,000 that had been there when he succeeded to the presidency in November 1963. His failure to honestly discuss how badly the war was going and to reveal the true costs of the conflict led to a credibility gap with voters. He also badly underestimated the determination of the enemy to win.
Meanwhile, the Great Society did make some historic achievements, such as providing the elderly with health insurance through Medicare, providing the money to spark economic development in the South, and extending civil and voting rights to African-Americans. But the momentum behind Johnson's programs stalled under the weight of the war's unpopularity and cost.
In the end, his overreaching in Vietnam and in the domestic arena were seen by Americans as vast and expensive mistakes. Amid rising antiwar protests and rebellions in his party, Johnson did not seek re-election in 1968.
More from our Most Consequential Elections series:
George Washington and the Election of 1788
Thomas Jefferson and the Election of 1800
Andrew Jackson and the Election of 1828
Abraham Lincoln and the Election of 1860
Abraham Lincoln and the 1864 Election
Theodore Roosevelt and the Election of 1904
Woodrow Wilson and the Election of 1912
Franklin Roosevelt and the Election of 1932
Ronald Reagan and the Election of 1980