We started down this path when Nixon wasn’t held to account for watergate. Then Reagan wasn’t held to account for Iran/contra. Then Clinton wasn’t held to account for lying about a consensual blowjob. Then baby bush wasn’t held to account for lying us into a tremendously expensive unsuccessful war of choice.
If trump isn’t held to account for attempting to overturn an election he knew he lost every future president will understand that there is absolutely no thing they could do for which they would have to fear accountability.