Final answer:
Lyndon B. Johnson faced criticism for intensifying the Vietnam War, leading to protests across the nation and influencing his decision to not seek reelection.
Step-by-step explanation:
The president who faced criticism and protest for intensifying US involvement in the Vietnam War was Lyndon B. Johnson. Johnson escalated the war by sending over half a million soldiers to Vietnam and was committed to a policy of slow escalation despite the turmoil it caused in the US. By 1967, America was deeply divided over the war, labeled with the terms "doves" and "hawks". The criticism peaked after the Tet Offensive, when public opinion shifted, culminating in Johnson's announcement on March 31, 1968, that he would not seek reelection. While Richard Nixon, who followed Johnson as president, campaigned on a platform that included a plan to end the war known as "Vietnamization," it was Johnson who bore the brunt of the public's disapproval during the war's intensification.