Chris,
The U.S. Government borrows money from the treasury market, ie, from the private sector, foreign governments and foreign central banks. It does not borrow directly from the U.S. central bank (Federal Reserve) under “normal” conditions.
(using “normal”, “central bank” and “U.S. Government” in the same sentence is hazardous.)
The central bank purchases short term U.S. Treasury notes, ie, with maturities less than 90 days in order to manipulate the amount of excess reserves in the banking system (The Federal Reserve System, the private banking cartel).
The amount of excess reserves determines the Fed funds rate (the rate banks charge each other for overnight loans). The Fed targets this rate. It keeps buying short term treasuries until this rate hits their targeted range. The larger the excess reserves in the system, the lower the Fed funds rate, the smaller the excess reserves, the higher the rate.
The central bank writes a check to buy the short term t-bills from those who hold them. This check is deposited into a commercial bank (usually one of the large money-center banks like JP Morgan). A demand deposit account is opened with money created from nothing. The bank has a “reserve” with the Fed (created from nothing), and the former holder of government debt has a demand deposit account that he can write checks on, to use as money.
Money created from debt. That’s how it works. Every penny of money in existence in the U.S. was created from debt using this mechanism.
Because of the Fed’s intervention, the banking system and the economy collapsed in Sept. 2008. Yes, the banking system actually collapsed. The TARP was needed to re-capitalize banks, and the TAG program was needed to guarantee all demand demand deposit accounts in the system (about $5 trillion, I believe, vs. the FDIC Fund of about $60 billion at the time).
(One of the large money market funds “broke the buck”, LIBOR rose to 6%, there was a run on the system, everyone wanted their “money” back all at once; the Fed would have had to print it all, causing a hyperinflationary collapse of the currency. Instead, promises were made to honor all accounts by the Central bank and U.S. Taxpayer; the market accepted this promise, and things calmed down, for now.)
Because the Fed funds rate is zero, the Fed now buys long term treasury notes in the open market using money created from nothing. For now, this has the effect of decreasing the yield on longer term bonds. This is called Quantitative Easing, a euphemism for money printing designed to prevent panic in the bond market, and keep excess reserves in the banking system increasing.
The U.S. Gov/t now runs $1.5 trillion annual deficits, with no end in sight. Buyers in the market place are insufficient to meet this demand. Without the Fed’s buying of these treasuries, yields would rise.
Higher bond yields would decrease the market value of the existing $13 trillion in treasury debt. This would cause a panic in the bond market as bond holders see the value of their investment drop. They might sell, causing yields to rise further, thus continuing the process of wealth destruction. The Fed would have to intervene to stop the process.
This is why the Fed is purchasing long term bonds.
The only “check” I can think of is the threat of a hyperinflationary melt down, caused by the Fed’s own printing. Paul Volker saw the beginnings of this process in the late '70’s, and actually tightened monetary policy to save the bond market. Fed funds peaked at about 20% in 1981, and I think treasuries rose to about 17%.
Sorry I used so many words, and maybe went beyond your question. But, there are many things going on when it comes to the Fed.
For an excellent explanation, read this: What Has Government Done to Our Money