It is my fond hope that Biden does investigate Trump - just not talk about that and deny any and all Trump investigations. If they find something then they can claim it fell into their laps and they were bound, by the law, to do something about it. I also, incidentally, believe Trump to be a criminal enterprise and also believe that they WILL find something.
I tend to doubt it, however. Biden is already saying that an investigation into Trump doings would not be a really good idea. I say, "fine" then stop talking about it and just let it happen! I can't even figure out why he would even talk about it! Just stirs the pot for absolutely no sensible reason.
My main fear is that what we are watching, in slow time, is the Democratic party beginning to work hard on their own failure. Trump has been investigating just about any Democrat he thinks he can go after and he does that publicly and his minions and true believers thinks he is doing a wonderful job. That being the case I would expect the Democrats would, at the very least, make sure that Trump has been on the up and up and, if not, hammer the crap out of him. I am praying that Biden doesn't take a leaf out of the Hillary book and just stand above the fray and never fight back or say a mean thing. That didn't work well for her and it sure as hell won't work real good for Biden. I fully expect, incidentally, that Trump is going to be constantly accusing the Dems of everything they can think of.