I may have jested about Trump selling them on eBay, but basically suspected something nefarious because he has no ethics and the whole thing seemed shady. His motivation for power might be similar to a beagle for bacon. I probably need more information to speculate on Biden. Because Trump seemed uncooperative it cast further suspicions and the nature of the documents that related to national security appeared to be concerning. I don't trust either's explanation yet, but it's a matter of degree if not magnitude.