The best description of the rhetorical technique employed by President Kennedy in the statement “Let us never negotiate out of fear. But let us never fear to negotiate” is:
The two sentences reflect each other in order to convey how powerful fear can be, even when people try to negotiate out of it.
This pairing of contrasting ideas highlights the complexities of fear in negotiation, emphasizing the importance of handling fear constructively rather than letting it dictate one's actions.