"Not all tax dollars are used to "pay down debt", actually nearly none are."
The debt is the aggregate of deficit spending in our history. Deficit, by definition, is spending - revenue, however, spending must occur prior to collection of revenue at the macro level or there is no "money" available to collect above that created by bank lending.
The government wants its own currency back, which is how it drives demand for it in the economy and controls the net money supply. The primary purpose of taxation has always been to enable the currency-issuing government to spend without "needing" revenue, not to provide revenue for spending. The US dollar is self-funding when it is spent into existence across the sectoral line between Treasury and the Fed by Constitutional authority granted to Congress.
As new dollars are created in the private sector they are tracked by the accounting entity of "debt" at Treasury and they become someone's monetary asset in the private sector. When dollars move in the other direction they can only go as far as extinguishing the debt they were created from. They are "uncreated" as soon as they enter the government's accounting sector and cannot then provide "funding" for anything.
Because law (Federal Reserve Act 1913) demands that any deficit spending be matched (not funded) with Treasury bond issues, the TGA account acts as a memo entry for tax and bond revenues. If new spending would push the account into negative Treasury must issue bonds for the difference/deficit before payments can be cleared at the Fed. You can see this replicated in your own bank account, if you have digital access to it, as memo deposits and debits that occur prior to any actual accounting of those items that would increase or decrease the physical amount of money you have.
The Treasury collects taxes, I write a check to the Treasury, when I get my SS payment that money comes from a Treasury account, just as did my Dad's Veteran Benefits checks. The Treasury balances payments it makes against payments received...what am I missing?
All federal spending is via new money creation. This is evident when Congress has its regular battles over spending and the debt ceiling. They always exempt these payments from the fight (and they always extend the ceiling after sufficient grandstanding for political impact). because they don't want the public asking why the taxes they paid into dedicated funds are not available without incurring additional debt above the ceiling. If the general public had a sudden such epiphany it might get ugly as they discover grandma didn't have to survive half of every month on cat food and veterans didn't have to be homeless.
It is more accurate to state that spending "funds" both taxes and Treasury bonds than the reverse when one understands the order of processes involved.
Alan Greenspan: "A government cannot become insolvent with respect to obligations in its own currency."
Ben Bernanke: "The U.S. government has a technology, called a printing press (or, today, its electronic equivalent), that allows it to produce as many U.S. dollars as it wishes at essentially no cost."
