Add together some of the biggest challenges U.S. banks weathered in the dozen years since the financial crisis, and you get an idea of how bad the coronavirus epidemic could be for them.

A decade ago, banks persevered through a recession and widespread loan defaults. Until 2015, they endured years of ultralow interest rates and slow loan growth that pressured their profitability. In 2015 and 2018, banks survived selloffs in the stock market. In 2016, the industry came through a collapse in energy prices with a few bruises,...