The State of New York, for example has an attorney general who said that there will be an investigation into Trump's activities. There are rumors that this type of action could eventually result in criminal charges and even prison time for the former president.
This has never happened before. The fact that this seems like such a case would be brought under state law means that we couldn't have, say Mike Pence or Ron DeSantis hand out a pardon like Gerald Ford did to Nixon. (And, New York is a heavily Democratic state, owing in large part to New York City's large population relative to the state).
The New York charges are centered around financial issues, which makes sense because that is where the state seems to have jurisdiction. If Trump was charged under New York financial law, what would be the political ramifications?
I know this sounds opinion based or an attack question, but there have been objective developments like the Mueller investigation (unrelated) and the Manhattan DA grand jury.