Shares in some of the world's biggest banks are plunging. Financial stocks in the S&P 500 are down more than 11% so far this year. That's worse than oil, energy stocks, and even the emerging markets index. European banks have fallen even further. Deutsche Bank (DB) has lost 31% so far this year, Unicredit (UNCFF) is down 35%, and Credit Suisse (CSGKF) is 30% down. Barclays (BCLYF), BNP Paribas (BNPQF), Societe General (SCGLF), and UBS (UBS) have all lost about 20% since the beginning of 2016. Bank earnings have generally been disappointing. Credit Suisse shares hit a 24-year low after...