The problem with Trump was that he wouldn't have been prosecuted if he had just handed them over. Outgoing presidents, and vice presidents usually don't do their own packing. That is even true for Trump.
The National Archives told Trump that there were missing documents, and to hand them over. He refused, and told them that the classified documents were party favors that he gets to keep and show off to his friends. All he had to do was hand them over, and none of this would have happened.
The Biden situation was a little different. When cleaning out a closet, aides found a small number of documents. Biden immediately informed the National Archives, had them take possession of the documents, and cooperated fully with the investigation.
It is interesting that no charges were brought against Mike Pence (and the documents were in his house), and no questions were asked regarding his mental acuity.
The same thing happened with Mike Pence, with the same end result:
DOJ closes Pence classified documents investigation with no charges
The Justice Department's national security division, which looked into the discovery of classified documents at the former vice president's Indiana home, informed his attorney that no charges will be filed.
https://www.nbcnews.com/politics/doj-cl ... -rcna87396
Former Vice President Mike Pence will not be charged in the discovery of classified documents at his Indiana home, according to a letter obtained by NBC News.On Thursday, the Justice Department's national security division informed Pence’s attorney that it had closed its investigation and that based on the “results” of that probe, no charges will be filed against the former vice president. Pence was interviewed as part of the DOJ's investigation, along with several aides, according to a source familiar with the matter.
Earlier this year, Pence’s lawyers said that a “small number” of classified materials had been found at the former vice president’s home in Indiana after the FBI discovered classified records
were initially discovered at a Washington think tank President Joe Biden used after he was vice president. The FBI later conducted a
five-hour voluntary search of Pence’s home, and uncovered another classified document. In the
case of Biden, Attorney General Merrick Garland named a special counsel — former Justice Department attorney Robert Hur — to lead that investigation,
but no special counsel was named in Pence’s case.