The current US Presidential campaign has had a lot of mud-slinging and accusations back and forth about violations of the law by the opposing candidate. One has explicitly stated plans to (if elected) instruct the Attorney General to appoint a special prosecutor to go after the other, some of whose supporters would likely support a similar plan if their candidate wins. (Edit: The candidate overtly making this pledge won the election.)
Are there any legal barriers to doing this? If so, what are they?
In general public policy terms, people are fed up with special treatment under the law for elites, but the US might block itself from getting high quality candidates in the future if it establishes a pattern of sending candidates to jail after losing elections. (Please, no comments on the quality of candidates in the present election.)