I still think if Biden ran as Vice president and Kamala Harris ran as president this would be a winning ticket

 Why?

Kamala Harris could debate circles around Trump because she is a very accomplished Debater. She was also the Attorney General of the State of California before being picked as Biden's Vice Presidential Candidate originally.

If Biden were in a support position he could advise her regarding world and domestic policies and she could debate and confront both of which he was not good at  (at least at this point in his life).