From the May 1 edition of ABC’s This Week with George Stephanopoulos:
MARTHA RADDATZ (HOST): And I want to ask you about her emails. You've been in government pretty much your whole life. Secretary Clinton has spent a good deal of time in government. I know there is lots of overclassification and people complain about that. But with your experience, if you read a document in an email, would you have a pretty good idea whether it should be marked Top Secret even if it wasn't?
ROBERT GATES: Sometimes not. The truth is, things are overclassified, and sometimes I would get something and it would be classified Secret or Top Secret.
RADDATZ: Even if it’s the highest classification?
GATES: And I would look at somebody and say, I'm about to tell a foreign leader what is on this piece of paper that's marked Top Secret. And that's going to do serious damage to the United States? Why are you giving it to me as a talking point if it's classified Top Secret? So it is tough sometimes. And if you don't have any markings on a piece of paper, it is tough sometimes to tell whether it's classified or not.