Most people hear "social engineering" and think of someone playing journalist to get access to places. The NSA's idea of social engineering is having the CIA work with the BND to buy Crypto AG.
Social engineering can be highly effective. However, from what we know about the NSA, especially from the Snowden leaks, it appears to be mainly a technical agency. It seems likely that the NSA does not use social engineering on a large scale itself but hands it off to other agencies like the CIA or the FBI.