It's groundbreaking since he doesn't think a formal Bible study among executive Cabinet members has been done in at least 100 years.
At which point the question becomes what is required to formalize a Bible study.
Set, regular time? Reserving a location? Predetermined syllabus?
I'd be pretty surprised if nothing similar happened during Reagan or either Bush's administration, but I'd expect it to be a much more impromptu, mostly Sunday thing happening more in response to folks being stuck in DC away from their home church on a given weekend.