When I worked for the Navy in the 1980s (civil service engineer) the security officer told us, "we don't care about weed, it's the beer of the 80s." Of course that was an era where having a couple of beers with lunch at the officer's club before going back to the office was routine.

I had two other jobs left that required pre employment drug screening, no random testing after hiring. I got the impression they were trying to weed out (no pun intended) people without the self control to abstain for a few weeks, but didn't much care beyond that if it wasn't a problem or on the job (one guy was fired for drinking in the parking lot on his lunch break).

As for drug testing for politicians, great idea! Give 'em a shot of sodium penthothal once a week and ask "what laws have you broken this week?"