Was President Kennedy's foreign policy a complete failure?

This is quite an interesting question as there's some really solid material to argue either way. You'd probably want to focus on the more prominent events of Kennedy's presidency - Specifically: The Bay of Pigs, Berlin Wall, the Cuban Missile Crisis and Vietnam. Some of these are more obvious fail/success cases. The Bay of Pigs, for example, saw 1,600 troops being captured or killed. I'd argue that this was a pretty clear failure. The campaign collapsed within weeks, and the US pushed Castro towards an alliance with Khrushchev. You could still point out that Kennedy's approval stood at 82% after the fiasco - however, from a purely foreign policy perspective, it's pretty easy to criticise. His handling of the missile crisis, on the other hand, is a fairly obvious success. Not only did Kennedy avert a potential nuclear war, but he also proved himself as a strong and capable leader. Prior to this, he hadn't really shown any leadshersip capabilities, and was widely considered a young and inexperienced President. The way he dealt with the crisis, whilst being a bit of a bluff, changed these attitudes. He had gone against the advice of his advisors, and it paid off. The incident saw the start of a hotline between the Whitehouse and the Kremlin, as well as the start of nuclear non-proliferation in the modern world. Beyond this, Khrushchev faced increasing pressures from the USSR and China to respond - his failure to do so would, eventually, lead to his downfall.
Vietnam and the Berlin Wall are more contested points. Starting with Vietnam, in terms of containment you could argue it was a success. The US managed to secure a strong presence in the South in preparation for the oncoming conflict. By the end of Kennedy's Presidency, America had over 20,000 'advisors' stationed in Vietnam, with this allowing swift action to be taken under President Johnson. On the other hand, Kennedy's presidency could be regarded as the beginning of America's failures. Firstly, his stationing of advisors can, in itself, be criticised - if you wanted to portray this as a success, the fact is that it wasn't actually Kennedy's idea. The programme was started by President Eisenhower, with Kennedy simply approving its continuation. This might not be enough to call his foreign policy a failure - however, it could be something you want to bring up if you were critiquing his 'successes'. Beyond this, the 1960 'Strategic Hamlets' programme saw a mass alienation of Vietnamese citizens. Uprooted Vietnamese were driven towards the Vietcong, with resistance to the US increasing as a result. From a containment standpoint, this was disastrous. Not only was the US failing in its attempts to prevent the spread of communism - it was actually doing the opposite. Finally, the fixing of Vietnamese elections by the US provoked outrage among the buddhist population - the cover of Rage Against the Machine's first album paints a pretty clear picture. This created unrest and significantly weakened President Johnson's later attempts to win over the 'hearts and minds' of the Vietnamese people, with the US being regarded as an essentially imperialist power. There's also some suggestion that the CIA was aware of the later plot to assassinate President Diem. His death plunged the country into more uncertainty, with America being criticised internationally for its lack of action. It was this that, arguably, served as a motive for future intervention, with President Johnson feeling some sort of responsibility towards the Vietnamese people. Like I said, Vietnam's up for debate - if you have time, you could spend most of your essay just talking about this.
The last point to consider is the construction of the Berlin wall. This one's interesting as it can be regarded as a success or a failure depending on who you ask. In the USSR, for example, Kennedy's apparent inaction was portrayed as a clear sign of weakness. The President was mocked in newspapers, with Khrushchev utilising the event as a means of consolidating the union. On the other hand, in the West, Kennedy's response was well received. His speech in West Berlin inspired a feeling of confidence, and propaganda in Germany displayed images of Russians 'hiding' behind their wall. Like most things in history, there are two different perspectives to consider. If you can do this, your answer won't just be more detailed - it will be more interesting.