First, he “misheard the question” may have been an honest answer but probably not the card you want to play too often when your candidate would be 78 the first day he occupies the Oval Office.
So far, Biden has pursued a much lighter schedule than the other candidates. He went an entire 10-day stretch recently without a public appearance, and those he makes are carefully choreographed. He largely has avoided the media or challenging interview settings.
It may be a smart strategy to a point, but the Rose Garden can become a Game of Thorns if the sense grows that the aging candidate is being protected from himself. The campaign is a proving ground to show he is up to the demands of the job.