Source: American Express, Facebook.

What: Shares of credit lender and payment processing facilitator American Express (NYSE:AXP) can't seem to catch a break, having dropped $0.12, or 0.2% on Tuesday to close at $81.91 following a rating downgrade and price target cut from research firm Macquarie.

So what: According to Vincent Caintic and Edward Odre, the two covering analysts at Macquarie who lowered their rating on American Express from "neutral" to "underperform" and cut their price target from $81 to $76, AmEx's near-term growth will be challenged by the loss of Costco Wholesale (NASDAQ:COST) as an exclusive partner and other negatives that may persist, putting as much as 21% downside pressure on shares, with only minimal upside potential of 7%.

Specifically, Caintic cautioned against holding American Express into its investor day meeting, which was recently rescheduled to March 25. Caintic suspects there could be talk regarding an antitrust settlement that day and is skeptical that AmEx can pass the Federal Reserve's annual Comprehensive Capital Analysis and Review.

Additionally, the analysts at Macquarie believe that in order for AmEx to return its pre-Costco account-loss levels, it would need to grow its top line by about 8% per year and its EPS by around 15% per year. Caintic did point out that AmEx's business outside of Costco has been strong, but intense competition will make it difficult for the company to even maintain market share in both the consumer and commercial segments moving forward.

Looking ahead to 2015 and 2016, Macquarie reduced its full-year EPS estimates to $5.39 and $5.63, respectively. The current consensus EPS on Wall Street is $5.51 for 2015 and $5.80 for 2016.

Now what: The question investors have to ask themselves here is whether or not the pessimism currently engulfing American Express is warranted.

Source: American Express, Facebook.

I'd opine that some degree of skepticism is warranted, as Costco represented about a tenth of AmEx's global cards in force in 2014, as well as 8% of its total billed business. It could be two or more years before we see AmEx establish itself as a growth company again.

Of course, there are also reasons to believe this dip is an attractive buying opportunity for the long run. With American Express likely to return to its roots by targeting affluent customers with its recognizable gold cards, it could once again build market share with a client base that's largely removed from the economic fluctuations of the U.S. economy. We also can't forget that AmEx thrives by double-dipping in growing economies as both a lender and a payment processor for merchants. So long as the U.S. economy is growing, AmEx has an opportunity to use that double-dip growth potential in its favor.

I certainly wouldn't fault investors here for taking a watch-and-wait approach until after the investor day meeting on March 25, but I don't see anything beyond a few speed bumps that should slow AmEx and its strong brand down over the long term.