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.

Investors haven't taken to the economy's uncertainty with much confidence to start the week as the Dow Jones Industrial Average (DJINDICES:^DJI) plunged into the red. The blue-chip index kicked things off with a gut-churning drop straight from the opening bell today, though stocks have recovered somewhat since then. As of 2:45 p.m. EDT, the Dow is down 85 points. Most of the index's member stocks are in the red today, but two leading names in the credit card business are digging deep holes for investors. Let's catch up on what you need to know.

Fear spikes, but credit card companies hold strong over time
(NYSE:V) and American Express (NYSE:AXP) aren't doing shareholders any favorites today, as the two credit card stocks are down 1.5% and 1.3%, respectively. It's not surprising that investors feel jitters about two consumer-reliant stocks as Washington's shutdown and the looming debt ceiling send jolts of uncertainty across the market. The market's "fear indicator," the CBOE Volatility Index (VOLATILITYINDICES:^VIX), or VIX, has jumped more than 10% today. The VIX has spiked by more than 15% in just the past five days and is at its highest point since June.

Ultimately, it's far more likely that these two government fights are short-term battles, though -- and American Express and Visa have been great plays in 2013, with each ranking among the top half of the Dow's stocks in year-to-date performance.

Visa's pulled down the stronger growth between the two despite its stock lagging against American Express. Visa's international operating revenues have soared over the past nine months. Excluding the company's Visa Europe segment, which has seen operating revenues fall by 2% over that time frame, the company's business outside the U.S. has jumped by 17% in the last nine months. Visa's U.S. operating revenues haven't exactly disappointed either, climbing 13% over that time.

The company's international strength should only help its stock delight investors over the long term, particularly as regions hard-hit economically (like Europe) regain their footing.

American Express hasn't posted the same sort of growth as Visa, but it's no slouch for investors craving stability and strong cash flow. The company continues to grow sales, as each of its four major business segments reported growth over the first half of 2013. Unlike with Visa, American Express' international segment hasn't shown astronomical growth recently; but the company's American operations continue to hum.

American Express' U.S. card services branch posted more than 4.6% sales growth over 2013's first six months, a strong showing for the company's largest segment by a large margin. American Express is known for catering more toward wealthier clients, and that strategy has helped it stay strong through the past five years despite the recession's effects: the stock's risen more than 220% over that time. This is one solid pick for the long term that won't fall to volatility, and despite today's losses, investors should feel confident about American Express' future as the economy rises.

Fool contributor Dan Carroll has no position in any stocks mentioned. The Motley Fool recommends American Express and Visa. The Motley Fool owns shares of Visa. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.