Summers' withdrawal followed growing resistance from critics. His exit could open the door for his chief rival, Janet Yellen, the Fed's vice chair. If chosen by President Barack Obama and confirmed by the Senate, Yellen would become the first woman to lead the Fed.
For months, the Fed has said it will slow its $85 billion-a-month in Treasury and mortgage bond purchases once the outlook for the job market has improved substantially. Those purchases have been designed to keep long-term loan rates low to get people to borrow and spend and invest in the stock market.
Super-low rates are credited with helping fuel a housing comeback, support economic growth, drive stocks to record highs and restore the wealth of many Americans.
Few think the Fed will significantly reduce its bond purchases — not now, anyway. Many economists think the Fed will announce when its two-day policy meeting ends Wednesday that it will slow its purchases by $10 billion — to $75 billon a month.
The pullback is expected to come from the Fed's Treasury purchases. It will likely maintain the pace of its mortgage bond buying to try to keep home-loan rates down to sustain the housing rebound.
Some had once expected a sharper first reduction in the Fed's purchases of around $20 billion a month. But that was before the government said that job growth was only modest in August and that employers added many fewer jobs in June and July than previously thought.
So why do economists think the Fed will reduce its stimulus for the economy at all?
In part, some Fed officials don't think the bond purchases are doing much good anymore. And they feel that by continuing to flood the financial system with cash, the Fed might be raising the risks of high inflation or dangerous bubbles in assets like stocks or real estate. Just the mention of a slowdown in bond purchases 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.