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Why Mastercard Stock Is Falling Today

Two of the nation's largest credit card lenders are merging, and some investors are worried about what the deal might mean for Mastercard (MA -3.04%). Shares of the global payment network processor are down 3% as of 10:30 ET Tuesday.Is Capital One buying its own rails?On Monday, Capital One Financial (COF 0.02%) announced it had made a deal to acquire Discover Financial Services (DFS 13.94%) for $35.3 billion in stock. The purchase is primarily about adding new customers for Capital One, but the company, wh ...