Moreover, according to a senior Democratic official, the party leadership would have much more control over choosing a replacement if Biden were to drop out after receiving the nomination than if he did so beforehand. Once a candidate is officially nominated, there is a process for the Democratic National Committee members to choose a successor. Biden is the dominant force at the DNC, and his preference for a successor would surely carry sway.

they want him to wait until at least after the convention, which up until now has been an unopposed victory lap, because after that, a window for a slightly-more-democratic process will be closed and bosses in the party can handpick someone.

If Biden were to exit before [the convention], his delegates might do what he asked of them — but they wouldn’t be bound in the same way they are now. In that scenario, the delegates could nominate anyone, and there could be a political brawl at the convention.

a "political brawl" is when a handful of national party bosses can't just appoint someone and would have to accept someone chosen by a larger group of people. Quelle horreur!

“We need to have as much discipline as emotion,” the senior Democratic official said. “It’s not politically smart for Biden to step down.”

lol, possibly the most nakedly self-serving quote in the entire article. "it doesn't work for my aspirations if i can't chose the nominee in secret with a handful of friends."