Currency and gas-price deflation have taken their toll on the company's results, but its warehouse-club model has so far protected Costco from the rising threat of e-commerce. With retailers ranging from Macy's to Target reporting lackluster results due to weak consumer spending, investors are hoping that Costco (NASDAQ: COST) will buck the trend when the company reports its fiscal third-quarter results on Wednesday. Costco is ending its longtime partnership with American Express next month in favor of Visa , a move that could expand its membership even further.