Doesn’t it all depend on what’s in the docs, both for Trump and Biden? If Biden’s documents are just routine, over-classified stuff that he might have taken home and forgotten, this will probably blow over. If those documents contain serious information that would benefit overseas interests, then this is just getting started and Biden is in big trouble. Trump too if that’s the case.
Both of them were careless idiots. Which one is worse depends on the content of the material they took.