John F. Kennedy was a senator before he -------------------- president in 1960.

The choice "elected" is grammatically incorrect in this context as it does not provide the necessary auxiliary verb to form the past passive construction. It lacks the verb "was," which is essential to convey that Kennedy was the recipient of the election action rather than the one performing the action.

"Was electing" is incorrect because it indicates an ongoing action in the past. This implies that Kennedy was in the process of electing himself, which does not align with the context of someone being chosen for a position. The sentence should reflect a completed action rather than a continuous one.

The phrase "had elected" suggests that Kennedy performed the action of electing someone else in the past, which does not fit the intended meaning of the sentence. The past perfect tense is inappropriate here since it implies an election took place before another past event, which is not applicable in this context.