Commentary  Previously, I explained how the Fed’s policy of buying and selling securities impacts interest rates and stock prices. The biggest change in purchases (or sales) in securities occurred from mid-2007 through mid-2008.  Then, the Fed sold 40 percent of its holdings of securities. The move reduced this component of money back to 1999 levels. This lack of money produced a liquidity shortfall, a collapse stock prices, and a collapse in the economy. In February, 2009, the Fed began repurchasing securities to restore money. The stock market began to recover in March. By April, the Fed not only had completely replaced all the securities it had sold, it added an additional $200 billion. By July, the economy began to recover. Over the next four years the Fed bought an unprecedented $3 trillion in securities. This brought its total holdings to just over $4 trillion, the largest increase in bank reserves …