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spooked investors. Some fear that the Fed's ultra-low-rate policies distorted the prices of some assets.
• In addition, the Fed eventually needs to sell its vast investment portfolio, which is on track to top $4 trillion next year, without upsetting markets. The more the Fed expands its portfolio, the harder and more perilous the eventual sell-off could be.
• And because the Fed has been raising expectations that its pullback will start as soon as September, some Fed officials may worry that defying those expectations would rattle investors.
• Finally, there's Bernanke's expected departure in January. If the Fed is going to slow its stimulus, officials may not want to wait until their last meeting of the year in December, just before a new chairman takes over. That's, in part, why some think a pullback in bond purchases will be announced Wednesday.

• "Bernanke may well want to have a bond-reduction program in place before a new chairman comes in," said David Wyss, a former chief economist at Standard & Poor's and now an economics professor at Brown University.
• All that said, it's possible the Fed will choose not to slow its bond purchases now. In recent public remarks, some Fed officials have sounded uncertain that the economy and the job market have improved enough.
• Once the Fed an

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