I don't think it's a deal-breaker for the government employees running the hiring process. Trust me, I know some UK civil servants and after the initial drugs test, most of them were very happy to resume their various indulgences.
The trouble is that you can't be seen to employ someone to work for the federal government when they are technically committing a federal felony.
I reckon the vast majority from the lower level employees to the higher ups would LOVE to have weed, LSD, and other recreational drugs at least de-scheduled if not legalised, regulated, and taxed.
It's politically difficult, especially in a country as socially right-wing as the US (on average, I'm aware attitudes vary from state to state).