The shock and tragedy of his assassination, and the grief so many felt about what his presidency might have been, has undoubtedly influenced many people in their assessment of his presidency. The Washington Post described him as "a brilliant rhetorician who inspired a generation of young Americans, and [whose] death left a lingering scar on the American psyche."
From the Cuban missile crisis and the Bay of Pigs invasion to a lackluster record on civil rights, Dylan Matthews argues in this Washington Post piece that JFK's presidency was vastly overrated.
At The Atlantic, Alan Brinkley argues that Kennedy's symbolic importance and the goals of his presidency may have outweighed what he actually accomplished—but they still made him great.
Kennedy was the youngest man ever elected to the presidency....He symbolized—as he well realized—a new generation and its coming-of-age....during his short presidency [he] proposed many important steps forward. In an address at American University in 1963, he spoke kindly of the Soviet Union, thereby easing the Cold War. The following day, after almost two years of mostly avoiding the issue of civil rights, he delivered a speech of exceptional elegance, and launched a drive for a civil-rights bill that he hoped would end racial segregation. He also proposed a voting-rights bill and federal programs to provide health care to the elderly and the poor. Few of these proposals became law in his lifetime....but most of these bills became law after his death—in part because of his successor’s political skill, but also because they seemed like a monument to a martyred president.
Brinkley also points to the poignant elegance of his speeches and his capacity to inspire as evidence of his greatness:
To watch him on film today is to be struck by the power of his presence and the wit and elegance of his oratory....He reminds many Americans of an age when it was possible to believe that politics could speak to society’s moral yearnings and be harnessed to its highest aspirations. More than anything, perhaps, Kennedy reminds us of a time when the nation’s capacities looked limitless, when its future seemed unbounded, when Americans believed that they could solve hard problems and accomplish bold deeds.
But others say the mythology surrounding his life, family and presidency is just that: a myth, and that his murder ensured he would be canonized in the popular imagination whether or not he deserved it.