Comment by anigbrowl

I think it's more analogous to the overlap between police and prosecutors. Those who are the object of regulatory enforcement can and do bring their objections to courts. Another difference is that agency rulemaking is not made in a vacuum; there's a pretty elaborate rulemaking process which includes (iirc) notices of proposed rulemaking, mandatory public comment periods spanning months, pre-publication of draft rules to allow the possibility of litigation and so on.