On Tuesday, ahead of the FOMC decision on Wednesday which most analysts expecting the FOMC to not do anything, the stock market traded sideways in a narrow trading range.
The pattern should continue until the FOMC officially announces their decision in the afternoon on Wednesday. After the announcement, the market could have a reaction, positive or negative, but I would expect buy programs should be very active, and any selling could be met with massive buy programs.
On any selling, 5595-5600 would be a strong support.