Hold on to your wallet: The Durbin Amendment goes into effect Saturday. The once-obscure amendment to the Dodd-Frank financial-reform bill limits “interchange fees,” which banks charge to merchants for providing the service that allows stores to accept debit-card payments. The fees were cut by some 80 percent, which makes it less profitable for banks to offer debit-card services. So the banks have done the natural thing and begun to transfer the fee from merchants to their customers, with Bank of America announcing a new $5-per-month fee for debit-card users. Naturally, the amendment’s author, Sen. Dick Durbin (D., Ill.) is in...