The back-to-school shopping season was not even over before some retailers came forward to temper expectations about the upcoming holiday shopping season. Biglike Wal-Mart Stores Inc., Target Corp. and Ross Stores, have warned that the second half of the year will be more difficult than the first. That's especially alarming considering the first half of the year has not exactly been robust. Same-store sales growth has averaged about 2.3 percent per month through July. Several retailers have cut full-year forecasts in light of the reduced expectations. When doing so, the companies have pointed to a number of reasons for the expected tough times ahead, including the deteriorating housing market, increasing fuel and food costs and economic uncertainty arising from the recent credit crunch and a volatile stock market.