Why would Trump go to prison? I think democrats will forget about him the moment he is out of office as he drifts into irrelevancy. I like to think of it like the time Trump promised a special prosecutor for Hillary Clinton. The moment he won, he dropped the act really quick.
The extremists in the Biden administration (such as Harris and those associated with Harris) want Trump in prison because they want to stomp out dissent, and want to prevent him from influencing voters. Unlike Clinton, Trump has a large base that is specific to him. Also, in the beginning of the Trump administration, Clinton largely was discrediting the Trump Presidency via proxies, while Trump will likely personally discredit the Biden administration.
A lot of people seem to be assuming Biden will weaponize the DOJ the way Trump has, I think that's very unlikely.
It may sound extreme compared to how Trump does things now, but there was a system in place to keep any decisions involving domestic law enforcement away from the president, and the president would go out of his way to only encourage broad strategies to his LE and intelligence agencies on anything domestic. Suggesting charges or an investigation of specific group, or business, or person or, worst of them all, a political person would be unheard of and a massive scandal. Not just Obama, every president for decades.
It's possible Biden tells the AG not to charge Trump, but I think the most likely situation will be Biden being as far away as possible from the decision. And I doubt his choice for AG will be based on anticipating how the nominee would deal with Trumps crimes specifically.