I’m not sure how thick that red line really is. I find it hard to believe that this IRS database is used strictly by the IRS and not shared with other agencies

I’m not sure how thick that red line really is. I find it hard to believe that this IRS database is used strictly by the IRS and not shared with other agencies (whether in the intelligence community or otherwise). Frankly it doesn’t even matter - the NSA could plant somebody in the IRS and get access to it anyway. Overall I agree with your premise. There are certainly some safeguards already in place. But even those aren’t foolproof (e.g. an IRS employee leaked 45’s tax returns to NYT). The data is collected and it’s indexed in an automated retrieval system. Any barriers to that will inevitably be circumvented.