Michael Hiltzik at the Los Angeles Times doesn't think much of the idea being floated by the Trump Administration of replacing the FICA tax that funds Social Security with some other tax. Hiltzik's rationale mostly comes down to the logic in this old quote from Franklin Roosevelt:
We put those payroll contributions there so as to give the contributors a legal, moral and political right to collect their pensions. … With those taxes in there, no damn politician can ever scrap my social security program.