Immediately after Kennedy's death, Johnson reached out to Eisenhower, with whom he had always gotten along. According to Gibbs and Duffy, Johnson leaned on the former president for help as Vietnam became more and more of an issue. When the decision to escalate troops in 1965 came, Johnson called Eisenhower. "You have to go all out," the former president told him, according to Gibbs and Duffy. "This is a war, and as long as they are putting men down there, my advice is 'do what you have to do.'"

Former presidents Lyndon B. Johnson (l.) and Dwight D. Eisenhower (r.)