Exactly. What system does the Census Bureau use to make certain that there are no nutjobs under their employ? The same one used by the Postal Service?
There are background checks and references, (that are actually contacted) and fingerprints of new employees; no convicted felons, etc. Obviously, the checks aren't to the level of say an FBI or CIA employee, but they're there.
And there are massive fines and long prison sentences for Census employess that divulge private info.