Very least it's easy to understand why the DoJ is involved. To borrow an analog found on Reddit:
The analogy I came up with:
Biden: Checks out a library book. Forgets to return it. Upon finding he still had it he returned it right away without being asked to do so.
Trump: Walks into a library right before his library card expires, grabs a shelf full of books, ignores the checkout lanes so he basically steals them as he packs them into his car, and when the library discovers what he's done repeatedly asks him to return the books. Trump lies and claims he doesn't have them, then refuses to return them, then the cops come calling and then grouses about how unfair it is and how he's been personally violated when they retrieve the books he stole.
Hah. Good analogy. Except poor librarians aren't allowed to call the cops on people who don't return their books.
What are the consequences for not returning library books? I never knew they couldn't do that.