Document mishandling can lead to a slap on the wrist if you let the investigators come in and take a look (Clinton, Biden), but if you refuse to give investigators access, and brazenly lie to them about the documents you still keep, then their only option is warrants and raids (Trump). Then they might indict you, but only about documents that you didn't hand back when they asked for them.

If we call every legal action against a political candidate political interference, we have two systems of justice, and all you need to do to have no consequences is to keep running for office. Then any investigations on you or your family become a witch hunt.

The mechanism to sort it out is that the data must come to light at trial, and people can make their own minds regarding whether the investigation did everything that was remotely reasonable to get cooperation or not. But then again, thanks to the US media environment that is more interested in entertaining than informing, people's opinions might have little to do with reality, thanks to their own political biases. That allows someone to, on the campaign trail, call for locking up the opposition candidate, while claiming that everything is a witch hunt when any investigation heads in their direction.