Stocks were still off Monday’s worst levels, but earlier rebound efforts have weakened. The S&P 500 and the Nasdaq were off 0.4% and 0.3%, respectively. Meanwhile, the Dow Jones industrial average fell 0.5%. Volume was again tracking higher on both major exchanges in the stock market today. Ctrip.com (CTRP) slumped 4% to its lowest levels since late June.