Economic worries both at home and overseas have U.S. stocks stumbling in morning trading. The Dow Jones Industrials lost triple digits off the start. Global equity markets are also down on fears of instability of Portugal's banking industry. The markets are also concerned the U.S. economy may be weaker than expected. Earnings are moving stocks today as well. Shares of Family Dollar (FDO) are down after the troubled discount retailer saw its third quarter profit drop. The company is under pressure from activist investor Carl Icahn to put itself up for sale. Potbelly (PBPB) is also trading lower after warning it expects weak sales for Q2. Costco (COST) is another stock to watch in today's session. TheStreet's Susannah Lee reports from Wall Street.