“The presidential debates are in effect already occurring daily between” Cuomo and Trump, Craig Snyder, a former Republican Senate chief of staff, argued in The Philadelphia Inquirer. We don’t have to suppose Democratic Party leaders have noticed; they undoubtedly have.
So if they wanted to replace Biden (whether with Cuomo, the veep nominee, or some arrangement of both) Democratic leadership could wait until after the nomination to do so. Then, as they did with Democratic vice presidential nominee Thomas Eagleton in 1972, they could ask Biden to step aside, citing his health.
Biden’s agreement is a long shot. Eagleton continued his Senate career after leaving the 1972 ticket over pressure about his mental health, but he was a much younger man. At Biden’s age, stepping aside would end his political career for good. Relinquishing the nomination would therefore suggest he expects an embarrassing loss and ruined legacy if he stays.
With Biden out, the Democratic National Committee, a group of around 350 which is “composed of the chairs and vice-chairs of each state Democratic Party Committee and over 200 members elected by Democrats in all 57 states and the territories,” would vote to select a new nominee.