Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

The Dow Jones Industrials (DJINDICES:^DJI) fell more than 30 points today, closing out August with its worst monthly performance in 15 months. As if the ongoing uncertainty about the state of the U.S. economic recovery weren't enough, heightened tensions in Syria have investors on edge about the prospect for a potentially costly military conflict in the Middle East, and the destabilizing effect it could have not only on the region, but on global trade generally.

In the face of that uncertainty, investors appeared to prefer stocks that they've traditionally turned to during past times of trouble. Wal-Mart (NYSE:WMT) was the biggest gainer in the average today, climbing three-quarters of a percent. For those fearing that a September swoon will follow August's bad performance, Wal-Mart stands out as one of the few stocks that managed to gain ground during 2008's market meltdown. Yet, before you assume that Wal-Mart can withstand another slowdown, it's worth noting that the retailer's latest quarterly report from earlier this month predicted slower sales growth than originally expected, as well as a cut in earnings guidance. Without a good back-to-school season, Wal-Mart's current quarter could disappoint defensive investors, as well.

Consumer-goods giant Procter & Gamble (NYSE:PG) almost matched Wal-Mart's gain, despite enduring yet another single-stock flash-crash event just after noon EDT that briefly sent shares down almost 5%. With its large stable of popular brands, P&G is able to resist drops in demand that less powerful companies often endure during slowdowns. Yet, the stock's price is fairly high already, with shares fetching more than 20 times trailing earnings. That removes some of the margin of safety that defensive investors rely on.

Finally, AT&T (NYSE:T) rose half a percent. With so much attention swirling around Verizon's (NYSE:VZ) potentially taking full control of its Verizon Wireless unit, some analysts have speculated that AT&T might try to take over the shell of current Verizon partner Vodafone after a Verizon Wireless deal takes place. Such a move would give AT&T the growth opportunities it has been seeking, as Vodafone has an extensive international presence in many important global markets. With antitrust concerns facing any attempt by AT&T to bolster its U.S. market share, looking overseas appears to be AT&T's only option for growth prospects.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.