Under Bernanke, the Fed has engaged in three rounds of bond buying to support the economy. Its investment portfolio has swollen to a record $3.85 trillion a¿¿ a four-fold increase since the financial crisis struck in 2008.Critics, including Republican lawmakers, argue that all the money the Fed has pumped into the economy is creating bubbles in stocks and perhaps other assets. Eventually, an asset bubble can pop with the same devastating effects that the collapse of the housing bubble produced. Some also worry that the Fed's bond buying is ensuring future high inflation. And they say markets will be vulnerable to turbulent swings once the Fed starts selling its portfolio. Investors will be listening for any comments from Yellen about the Fed's exit plans and whether she's considering safeguards to protect the markets and the economy from turbulence.