Heres the thing with failing drug tests. 99% of the time you take a test it comes after someone has already asked you if you do drugs. If you said "why yes, i smoke pot all the time" they probably arent going to bother testing you. So, if you get a possitive test that likely means that you lied to your recruiter or another official about your drug use. More than anything else, lying like that is probably a bigger deal since its speaks more to character than the actual drug use itself. In other words, it might be more important that he lied about his use than that he did it in the first place.