Whitmer, klobuchar, newsom , Warnock, pritzker, hell i'll even take buttigieg, literally anyone on the 2020 debate stage before the center collapsed in on Joe Biden after Obama told them too.
What campaign, he's literally running on being better then trump and he still somehow failed at that, put anyone else on that debate stage and Trump would've been cooked. What is bidens personal selling point? His platform is the standard democrat party line, he's an old white man from a solid blue state so he's not bringing any constituencies from his identity, he's even lost his wise elder statesman angle after that last debate. If you put any other democrat in they could not be trump just as well if not better then Biden.