The "mixing" (or lumping together) of money (revenues & deficits, including SS) has been the R's framing of the issue all along. They dismiss the solvency of the SS Trust Fund by lumping the payroll taxes together with all revenue and talking about SS payments to retirees (current and future) in the context of the larger deficit issue. They conveniently ignore the "structure of the program" you refer to.
...is going around in circles. Yes, that has always been the RW spin, but it's bogus. So why are people trying to argue it now?