This seems like answers could be highly subjective. But JFK did choose to not invade Cuba against the wishes of the Joint Chiefs. An invasion would have caused nuclear war (from the personal recollections of Robert McNamara in The Fog of War).
While Kennedy did not have much success passing his initiatives. In his famous 1963 speech "Let Us Continue" LBJ promised to fight for everything JFK wanted. This included Medicare, civil rights act, the Peace Corps, War on Poverty, Food Stamps, Voting Rights Act, a number of job and education initiatives...the list goes on.
Its a difficult question because JFK was unable to pass his initiatives, but LBJ did. These laws have far reaching impact to this day. Whether they are all positive is a matter of intense political debate from their passing until now.
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Thank you.
"Good" is subjective, but Gallup lists some stats about their polls collected during their presidency. He had an average approval rating of 70.1% (higher than any other president since the data starts with Truman), a high of 83% (second only to George W. Bush during September, 2001) and a low of 56% (higher than anybody on the list, and the only president listed to never dip below 50%).
Here's a graph of the approval ratings throughout the presidency.
So based on polls during the time period, he was definitely popular and well-liked at the time. Kennedy's high in April, 1961 came after he famously took responsibility for the failed Bay of Pigs invasion (and when he did a celebrated job throwing out the first pitch of the 1961 Major League Baseball season, but I can't find enough data to be sure which event caused the spike), and he had another huge jump in late 1962 after the peaceful resolution to Cuban Missile Crisis gave everyone a reason to talk about "cooler heads."
There are definitely a few memorable moments during the Kennedy presidency, and he was definitely well-liked, but as far as lasting actions? He created the Peace Corps, signed the Partial Nuclear Test Ban Treaty, increased government spending during huge economic growth, supported civil rights without having huge battles over civil rights legislation, and boldly declared the US would land a man on the moon (and get him back safely) by the end of the decade. Most of those things sound mostly good to most people, probably, but I can't say what makes someone good.
"Good" and "Bad" presidential judgments are so subjective it's almost not even worth considering. Additionally, they have a delayed effect on future administrations (e.g. Reagan was a "good" president because he cut taxes without cutting spending, while Bush was "bad" because he tried to reduce the deficit which Reagan left him, etc).
Surely JFK has received some sympathy in the public mind due to the circumstances of his death. Every city would not have a John F Kennedy school or highway, or JFK airport in NY would not be named after him had it not been for his assassination. That being said, let's look at his actual record.
Upon taking office, he is pressured into supporting the planned invasion of Cuba which became known as the Bay of Pigs. He doesn't want to use actual American units for political reasons, so it is largely a covertly supported CIA mission using a small number of Cuban expats. Information about the operation leaks and Castro is prepared to defend his island. The mission is a failure, and Kennedy feels like he got suckered by the Joint Chiefs. In a move that would be unprecedented by today's standards, he publicly takes responsibility for the failure. Far more importantly, he learns from it, and applies the lessons to...
The Cuban Missile Crisis. In 1962, prompted largely by Castro's requests, US inflexibility on Berlin, and a certain amount of hubris that can not logically be explained, Khrushchev moves to place nuclear missiles in Cuba. Remembering the Bay of Pigs fiasco, Kennedy rebuffs the hawks in his own administration who advocate airstrikes against Cuba followed by an invasion, and through two long weeks manages to come to an agreement which is acceptable by both sides. Because the Soviets remove the missiles, Kennedy and the US are seen as the "winners", even though both sides got something they wanted.
Vietnam - Kennedy has gone down in history as a hawk in Cold War politics, but this is not entirely fair. As Thurston Clarke's book JFK's Last Hundred Days notes, Kennedy was very lukewarm about sending additional forces to Indochina, and was doing so only for political reasons. He had every intention of withdrawing US forces following the 1964 election.
Civil Rights - This is seen as the weakness of Kennedy's administration, and an issue largely deferred until the Johnson era. Again, this is the delayed effect of presidencies. Had Kennedy not died and Johnson reaped the political capital which came from it, he would not have had the power to push the Civil Rights legislation that he did. Credit should also be given to Johnson as a storied negotiator who could charm anyone into voting his way on almost anything. For Kennedy being a Yankee Democrat in a party which depended upon Southern support, his actions and words in regard to Civil Rights are quite impressive.
Domestically - Kennedy oversaw a relatively strong economy and robust employment. However, this is largely a function of the business cycle and post-war US hegemony than any one president's policies.
Overall we could say that Kennedy's handling of the presidency, and in particular his willingness to learn in office, were above average.
The book Between a River & a Mountain by Edmund Wehrle goes into detail about one of the JFK administration's major goals: establishing labor unions internationally. The book describes how the administration used economics and social welfare, not warfare, to push back the tide of Communism that was yearning to fill the power vacuum left after World War II. By creating stability in third world nations through these labor unions with the help of the AFL and the CIO, JFK and his administration achieved the objective of the Cold War, to hold back Communism, and also achieved the JFK administration's personal goal of doing so through peace. This method was further accentuated by the Peace Corps.