One of the most vivid memories of the Great Depression is the sight of nervous depositors lined up outside a bank hoping to withdraw their meager savings before the bank failed.  Like a rare tropical disease that was thought to be eradicated by modern medicine, the classic bank run reappeared this month in the form of Silicon Valley Bank.  At the beginning of March, the market had no particular concerns about the potential for systemic bank failures, but SVB’s sudden demise has cast a pall over the entire industry.