I think much of the 6.5 trillion is due to a failed, inadequate accounting system. The number is too large to have any degree of accuracy attributed to it since that much money was never appropriated by Congress in the first place. No doubt some small portion of it is real and has been siphoned of illegally by defense contractors who were paid for services and weapon systems they didn't provide. By definition the black budget can't be properly tracked as the accountants aren't given access to details.....just gross totals and who knows what got counted. Government is just so big that accuracy is not possible anymore. Personally, I ascribe to the principle that if more than 1000 people are involved in accounting for anything then their combined output product is almost guaranteed to be suspect.