It's remarkable that so many people have already forgotten what happened in 2020. The Democratic Primary was an absolute slog, it all just seemed so negative and messy ... and then over the course of about 48 hours, everything crystalized around Biden, the negative vibes were gone from everyone except the most hardcore Bernie supporters, people got excited again, Biden soared in the polls and it snowballed into an 8 month campaign of optimism.
Everything changed in 48 hours, and all it took was a handful of important people - led by Jim Clyburn - emphatically getting behind Biden. THE EXACT SAME THING could (and likely would) happen with Kamala if Biden bows out and emphatically endorses her.
This isn't complicated. There is nothing Biden can do for himself to give the Democratic Party the shot in the arm it sorely needs, but he can absolutely play the 2024 version of Clyburn and fulfill his stated goal of being a transitional president. Just do it, Joe.