As revealed by the failures of three regional banks in the spring of 2023, bank runs are not a thing of the past. To inform the ongoing discussion of the appropriate regulatory response, we examine trends in the banking industry over the last twenty-five years. On the liability side of bank balance sheets, deposits—and especially uninsured deposits—have grown rapidly. On the asset side, there has been a notable shift away from the information-intensive lending traditionally associated with banks and toward longer-term securities such as mortgage-backed securities and long-term Treasuries. These trends appear to be related, in the sense that banks with the most rapid growth in deposits have seen the biggest declines in loans as a share of assets. Thus, while the banks that failed in early 2023 were arguably extreme cases, they reflect broader trends, especially among larger banks. We construct a simple model to help assess the main regulatory options to reduce the risk of destabilizing bank runs—expanding deposit insurance and strengthening liquidity regulation—and argue that the industry trends we document favor the latter option. Using the model, we offer some design considerations for modifying the liquidity coverage ratio so as to require banks to pre-position sufficient collateral—largely in the form of short-term government securities—at the Federal Reserve's discount window to ensure they have enough liquidity to withstand a run on their uninsured deposits. We also comment briefly on some other regulatory implications of our findings, including for interest rate risk regulation and merger policy.

正如 2023 年春季三家区域性银行的倒闭所揭示的那样，银行挤兑并未成为过去。为了为正在进行的适当监管应对措施的讨论提供信息，我们研究了过去 25 年银行业的趋势。在银行资产负债表的负债方面，存款（尤其是无保险存款）增长迅速。在资产方面，传统上与银行相关的信息密集型借贷已发生显著转变，转向抵押贷款支持证券和长期国债等长期证券。这些趋势似乎是相关的，因为存款增长最快的银行的贷款占资产份额的下降幅度最大。因此，虽然 2023 年初倒闭的银行可以说是极端案例，但它们反映了更广泛的趋势，尤其是在大型银行中。我们构建了一个简单的模型来帮助评估主要的监管选项，以降低破坏银行挤兑稳定的风险——扩大存款保险和加强流动性监管——并认为我们记录的行业趋势支持后一种选择。使用该模型，我们提供了一些修改流动性覆盖率的设计考虑因素，以便要求银行在美联储的贴现窗口预先配置足够的抵押品（主要以短期政府证券的形式），以确保它们有足够的流动性来承受其未投保存款的挤兑。我们还简要评论了我们的研究结果的其他一些监管影响，包括对利率风险监管和合并政策的影响。