Democratic leaders have stood by the president as he faces questions about his ability to defeat Trump in November. But privately, many are expressing concern.

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.

If Biden were to exit before that, 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.