In general I’m always surprised at how often the two main parties in US allow senior politicians to have multiple cracks at the top office, and allow in fighting to lessen the chances of ultimate victory in main election.
In UK..Conservative party is particularly ruthless in dealing with politicians that fail to win General Elections..the men in grey suits just ask the loser to retire to their country estates. The Labour Party isn’t much less ruthless...maybe finding the loser a well paid sinecure somewhere.
Certainly it’s hard to imagine that multiple losers like Hilary C, Bernie S, or Uncle Joe being allowed anywhere near a party leadership contest.