Explanation

“Badly miscalculated” indicates that there are two opposing parts of the sentence: the candidate’s “prepared speeches” are good, but some other type of answers are bad.

You need two words that mean “improvised” or “off-the-cuff.” Note that lubricious and disingenuous form a pair relating to dishonesty that is unrelated to the clues and might be a trap (if you insert your own, negative ideas about politicians). Premeditated is the opposite of what you want.

Hence options Extemporaneous, impromptu are correct!