You want to bet the reason Obama is not endorsing Quid Pro Joe is because Obama knows of all the things Trump can tie around his neck that happened on Obama's watch. That's why Obama didn't want Joe running in the first place. In 2016, he listened to Obama, and didn't run. But since Bernie was going to destroy the party if he got the nomination, the Deep State convinced him to run in 2020.
This is no surprise. The greatest fraud ever was a traitor is a traitor and continues to be a traitor. The question is will he be held accountable for his many and continuing crimes.