A bond is not “money”, meaning that new money must be created to pay benefits. The bond is a “promise to pay” at a future date, not a depository for existing money. Beneficiaries pay a portion of their wages for a “legal claim” to those future payments, but their payments are don’t do anything to make it easier for the government to pay benefits as the federal government always has an infinite number of US dollars available to it.

This holds true whether revenue is collected for the system or not. Bonds only remove “money” (reserves) from the banking system so they are not a funding mechanism for federal spending. A government that claims it is paying itself interest in a fiat currency is conning its people.