Image: Wal-Mart.

Stocks struggled to move much in either direction Tuesday morning, as investors have become uncertain about whether the stock market can continue its record run or whether it will finally succumb to a long-overdue pullback. As of 11:40 a.m. EDT, the Dow Jones Industrials (DJINDICES:^DJI) were up about 15 points, but broader market measures were close to unchanged.

One sign of investors' uncertainty has come from the most recent earnings season, in which pockets of strength and weakness have made it hard to draw firm conclusions. Just this morning, very different results from Wal-Mart (NYSE:WMT) and Home Depot (NYSE:HD) pointed to the tug-of-war going on in the U.S. economy and the stock market. Let's look at what these two retailers said in their earnings announcements and what they suggest about the future of the national economy more broadly.

Wal-Mart falls short while Home Depot builds higher
Among the two big-box giants, Wal-Mart was the clear loser, with its stock falling more than 4% after the retailer announced its fiscal first-quarter results. Earnings of $1.03 per share were down more than 6% from the year-ago quarter and missed the consensus estimate among investors following the stock. More worrisome for some, though, was Wal-Mart's tepid 1.1% same-store sales gain for the quarter. The well-publicized raise in Wal-Mart employee wages pushed overall costs higher and operating income lower, and adverse currency fluctuations also hit earnings by about $0.03 per share. Overall, consolidated revenue at the big-box retailer fell 0.1%. Despite gains in the company's e-commerce sales, many Wal-Mart shareholders remain worried about whether it can continue to grow even with U.S. consumer standards of living rising again after the long recession.

Interestingly, Home Depot gave up its early share-price gains, falling just less than 1% as of 11:40 a.m. after initially climbing as much as 2%. Early spring is a key season for the home-improvement retailer, and a 6% revenue spike reflected better weather conditions that drove results. Comparable-store sales jumped more than 7% within the U.S. and 6% systemwide, with earnings topping estimates. Higher customer traffic contributed to the solid results, with the company seeing improvement in the housing market and in consumer sentiment generally. Home Depot also boosted its guidance for the remainder of the year, citing encouraging conditions and a promising outlook for housing.

It's dangerous to try to extrapolate broad trends from a couple data points, but the Home Depot and Wal-Mart results point to long-held trends at both companies. Home Depot has done a good job of maintaining its independence from economic conditions, with its stock soaring even when the housing market was lagging the recovery in the remainder of the U.S. economy. By catering both to professionals and to do-it-yourself homeowners, Home Depot found niches for success even when homes weren't selling well.

Meanwhile, changing demographics and business dynamics have squeezed Wal-Mart hard. In the past, Wal-Mart had a stranglehold on the lower end of the retail market, competing well on price. Yet the rise of deep-discount dollar-store retailers took away a key class of customer from Wal-Mart, and big-box competitors have sought to offer customers a more premium experience as a means of achieving wider margins and better profitability.

Overall, though, the fact that both these stocks proved unable to post lasting gains suggests investors are increasingly uncertain about the sustainability of the bull market. Even with stocks at record levels, investors should look closely at their risk levels to make sure they aren't excessively exposed.