No SSI is a
totally different animal.

As I said, since 1968 it is really all the same animal. SS is comingled with
the general fund. Right now that means the $140 billion dollar surplus is
dumped into the federal operating budget. In a decade or so that will become a
deficiet and will have to be made up by increased taxation somewhere (AKA
redeeming the bonds).
Which of this money is "Social Security" and which is "general fund". The
difference is totally in how the polititians sell the program in question.