What will Biden do?

The oddities of Joe Biden’s third presidential campaign are impossible to ignore. He is the oldest man ever nominated by a major political party, and the first nominee since 1992 to lose both Iowa and New Hampshire. He has been in seclusion inside his Delaware home since March, rarely venturing out of his basement. After winning the primary as a moderate, he has tacked left for the general, reversing the traditional sequence of presidential nominees.

Nor has Biden played it safe as his lead grows over President Trump. On the...