By The Associated PressWASHINGTON (AP) â¿¿ The Federal Reserve has taken many unprecedented steps in the past four years to try to boost the U.S. economy and counter the effects of a financial crisis that triggered a painful recession. It has kept the short-term interest rate it controls at a record low near zero since December 2008. It's bought more than $2 trillion in U.S. Treasurys and mortgage bonds to try to hold down longer-term rates. Those purchases have increased the Fed's balance sheet to more than $2.8 trillion. Some steps the Fed has taken: â¿¿ Nov. 25, 2008: The Fed says it will buy $500 billion in mortgage bonds. â¿¿ Dec. 15-16, 2008: The Fed creates a target range for interest rates and cuts its key federal funds rate to between zero and 0.25 percent. That's a record low. The Fed vows to use all the tools it has to rescue the economy from the worst financial crisis and recession since the 1930s. â¿¿ Jan. 27-28-2009: The central bank signals it's prepared to buy longer-term Treasuries and expand other programs. â¿¿ March 17-18, 2009: The Fed says it will start buying up to $300 billion in government bonds over six months. It also decides to boost purchases of Fannie Mae and Freddie Mac mortgage-backed securities and debt. The actions are aimed at driving down rates on mortgages and other debt. â¿¿ Sept. 22-23, 2009: The Fed slows a mortgage-buying program to complete its purchases by March 31, 2010, instead of at the end of 2009. â¿¿ Aug. 10, 2010: It decides to use some money generated by its mortgage portfolio to buy government debt, to try to lower rates on mortgages and other loans. â¿¿ Aug. 27, 2010: In a speech in Jackson Hole, Wyoming, Chairman Ben Bernanke lists several options to boost the economy, including the purchase of additional government bonds.