The "pool of money" idea itself has got to go. Government spending and revenues operate much more like sources and sinks than a purse.

Spending injects money into the economy and revenues extract it. The two roughly balance each other but only because overspending/undertaxing increases the money supply in negative ways and under pending/overtaxing decreased the money supply in other negative ways. Besides these, interest rates are the third lever of the economic engine.

The constraint is inflation rather than solvency for states who have monetary sovereignty.

I get the appeal and the logical, rational appeal of the purse model, but it leads to a warped idea of how the government and economy interact.