According to ABC news, all former presidents "[continue to receive] the President's Daily Brief, a top-secret summary of US intelligence and world events, in a format and style that suits them". This is supposedly a "courtesy" (see).
What is the rationale behind continuing to provide former presidents the PDB? Is this not an (unlikely, but potential) national security risk? How is it delivered, securely? Where is it stipulated that former presidents should continue to receive this information (the Former Presidents Act?)? Of what use is it to those who receive it?
I imagine there is a lot we don't know. What do we?