From dshort.com
"The Fed already buys and sells foreign exchange to prevent disorderly conditions in foreign exchange markets. The Fed has assumed a similar responsibility in the market for government securities. The Fed could support the stock market directly by buying market averages in the futures market, thus stabilizing the market as a whole. The stock market is certainly not too big for the Fed to handle." Robert Heller, Federal Reserve governor, WSJ, Oct 27, 1989