So, if we're talking about details and context: if the person involved is, in fact, the top classification authority (even if he has only a vague idea about the rules of classification), and has decided that letters from other heads of state are now unclassified, those documents then become unclassified, correct?
Removing political bias in the analysis: The Trump case is most likely that the sitting president decided to declassify certain documents that he wanted as momentos and then got cockly and arrogant about "his" momentos (oh, the ego on that moron) that he most likely declassified with a verbal order only (which is technically legal, though very poor procedure), while the Biden case is most likely that the non-sitting ex-vice president...or more likely his staff...unwittingly moved and stored classified documents inappropriately.
Like it or not, the Trump case was, at least in theory, possibly legal. The Biden case was most definitely not.
Both, in my book, were violations of proper processes (verbal declassification is only supposed to be used as an expedient, and should be followed by the written process) and should be investigated as such, intent or not.
I see no malice in either case. Lets face it, neither of those old guys was salivating over nuclear secrets or special intel. It was ignorance and arrogance in both cases.
If the legal process is completely fair, should there not be an FBI search of Biden's house? Especially considering that his son may have had direct access to said SAP documents?
But instead of logic and reason, let's go ahead and analyze things with our Red or Blue glasses on instead, because that makes things so much better...