Current NSA director Keith B. Alexander and Director of National Intelligence James R. Clapper Jr. have resolutely refused to offer an estimate of the number of Americans whose calls or e-mails have thus made their way into content databases such as ­NUCLEON.

The agency and its advocates maintain that its protection of that data is subject to rigorous controls and oversight by Congress and courts. For the public, it comes down to a question of unverifiable trust.