The FBI actively hires plenty of people that have smoked pot in the past, this was relaxed 8 years ago from the hard NO POT stance they had because of the above. In fact last time I was contacted by a recruiter I specifically asked about it and he said as long as you haven't used recently and state you're not a current user, you would be fine. Their clearance process is also run by them as with most agencies so consistency isn't always a thing. The most common component is OPM, beyond that adjudication rules and requirements are at the sole discretion of the acting entity. I won't go into specific waivers within other agencies, but I know first hand they're pretty common as long as you're not active military (even then there are always exceptions).

All said, I think the only real issue for a pass is law enforcement and their it's a gateway drug perspective. I also think that states will push back due to their perceived loses in fine revenues (because everyone knows the police should generate revenues right?).