Final answer:
Lyndon B. Johnson chose not to run for re-election in 1968 due to the fracturing of the Democratic Party, his declining health, and the significant unpopularity of the Vietnam War. Eugene McCarthy's strong antiwar stance and Robert F. Kennedy's entry into the race evidenced the party's divide. Johnson's decision was announced on national television on March 31, 1968.
Step-by-step explanation:
Why Did Lyndon B Johnson Not Run for Re-election in 1968?
Lyndon B. Johnson faced multiple challenges that led to his decision not to seek reelection in 1968. As the Vietnam War spiraled, becoming increasingly unpopular at home, the Democratic Party began to lose its internal cohesion. The New Hampshire primary was a pivotal moment, where Minnesota senator Eugene McCarthy, who campaigned with an antiwar platform, surprised the nation by nearly equaling Johnson's vote count. This strong showing from an antiwar candidate revealed a fracture in the Democratic base and foreshadowed potential difficulties for Johnson had he chosen to run.
Adding to the fray, Robert F. Kennedy entered the race, further dividing the party. Meanwhile, the Tet Offensive had a significant impact on public perception of the war. Influential journalist Walter Cronkite's pronouncement that the war was unwinnable deepened the despair and dissatisfaction among the American populace. Confronted with declining health, a party divided, and a war that had severely damaged his popularity, Johnson made a dramatic televised announcement on March 31, 1968, declaring he would not seek or accept the nomination of his party for another term as President.
The political landscape was also shifting nationally. Conservative ideologies were gaining traction, as seen in the previous election against Barry Goldwater. Despite his strong win in 1964, Johnson's appeal by 1968 had been tarnished, essentially due to his Vietnam policies. Realizing that his bid for reelection might lead to deeper divisions, Johnson stepped aside, a move that many saw as an effort to focus on peace negotiations without the complications of an election campaign.