Joe Biden’s self-inflicted electoral crisis is a classic case study in the “sunk cost fallacy.” As Vice President Kamala Harris and party leaders pour resources into the president’s flailing campaign, the argument that Biden is the only one who can defeat Donald Trump in November and “protect democracy” is increasingly falling on electoral and donor deaf ears. Coined in 1980 by economist Richard Thaler, the sunk-cost fallacy describes a cognitive bias that leads people to double down on failed strategies in which they have invested time, resources and emotional energy. Thaler used this concept to describe the irrational decisions that...