I believe there is financial assets that they have somehow legally maneuvered off the books.
Take Joe Bidon, (please!). He has been using Hunter and his brother to hide his wealth from selling corruption. Should he retire and claim that wealth, it will be unquestionable as long as he has paid the tax upon receiving it.
The papers were found to include the long missing joint income tax filings of Bess and Harry -- and what a tale they told. There were all sorts of irregularities in unreported assets and income. Harry and Bess even pocketed much of the Presidential expense allowance -- while Harry was complaining that it was inadequate and that he was going out of pocket. Congress dutifully raised the allowance.
As bad as Biden is, Lyndon Johnson was much worse, with numerous corrupt schemes that enriched him and his family. There is even a story to the effect that he had a hit man on call and arranged the murder of a Department of Agriculture investigator who had obtained proof linking Johnson to the massive Billie Sol Estes fraud. And Johnson has even been fingered as setting the murder of JFK into motion and orchestrating a cover up via the Warren Commission.
Jack Kennedy was also a crook. While President, he ran into a cash crunch due to high spending on his compulsive catting around and Jackie's expensive lifestyle. In order to raise cash, Kennedy shook down lobbyists and old political friends. One of them discussed going to the Kennedy compound at Hyannisport to deliver a briefcase full of cash. Kennedy accepted it without a word of thanks and tossed it into a closet full of such briefcases.