Bay of Pigs, Cuban Missile blockade.
JFK ordered the Bay of Pigs attack and then withdrew air support and let them get slaughtered, his incompetence then led to us to facing nuclear war during his blockade as he made Castro’s Cuba permanent and then starting the Vietnam war, and of course instead of tearing down the Berlin Wall, they built it during the disastrous Kennedy years.
He made Jimmy Carter look like a foreign policy whiz kid.