When you described trust funds as follows:
“- - - There are but they contain no assets, just unfunded liabilities backed by the full faith and credit of the US Treasury.”
then how does your description differ from a journal entry of debt?
"When a trust fund receives payroll taxes or other income that is not needed to pay benefits immediately, the Treasury credits the fund and uses the excess cash to reduce the amount of new federal borrowing that is needed to finance the governmentwide deficit. That is, if other tax and spending policies are unchanged, the government borrows less from the public than it would in the absence of those excess funds. The reverse is the case when revenues for a trust fund program fall short of expenses. Thus, the balances of trust funds are not a measure of resources available to pay future obligations for the respective programs; those resources will need to come from federal revenues or additional borrowing in the years those obligations are due."