George W. Maschke wrote on Jun 2^nd, 2017 at 1:50pm:

It is true that in order to be hired, one must pass both the polygraph and background investigation. But one can be rejected over either one, alone.

Correct.  As I've said numerous times on this site, the BI can be every bit as pernicious as the polygraph.

Certainly that was the case for me.  It was a great lesson for me in just how nasty people can be when they believe that they can hide under the cloak of anonymity.  One alcoholic sociopath who participated in my BI didn't even want anonymity! 

Following any rejection from any federal employment involving the almighty security clearance, always make a FOIA/PA request to the agency that ultimately declined the employment application.  Many applicants will be in for some very ugly surprises, as once was I. :o ::)