Currently both are funded through the FICA and Medicare taxes. Trump said yesterday that if he is reelected then he wants to eliminate both. Remove the funding and how do you continue the programs? What alternative sources are there?
Unused salaries and benefits of the several hundred thousand fired federal "employees".
Sales taxes. VAT. Tax on financial transactions. There are many ways to replace the revenue. See what is viable politically.
Currently, over 70% of earners pay more in payroll taxes than income taxes.