Public Liquidity and Financial Crises

U.S. Treasuries and bank reserves do more than finance the government or implement monetary policy. They are public liquidity: safe assets that private financial institutions can hold when they need protection against funding stress. This paper studies how the supply of public liquidity affects financial crises.

The basic mechanism is liquidity insurance. Banks borrow from households through insured deposits and runnable debt. In a crisis, some funding can be withdrawn. If banks hold enough public liquidity, they can meet withdrawals without selling productive assets at fire-sale prices. Public liquidity therefore makes the financial system more resilient to liquidity shocks.

But the effect is not one-sided. When the government supplies more liquid assets, banks hold more of them, crisis losses fall, lending can expand, and output can improve. At the same time, public liquidity can crowd out private liquidity, including bank deposits, and can encourage banks to operate with more leverage. That makes banks more vulnerable to other kinds of shocks, especially shocks to asset values rather than funding liquidity.

The paper builds a general equilibrium model in which banks demand public liquidity as insurance against crises. The liquidity premium on Treasuries is the price of this insurance: investors accept lower yields because Treasuries help protect against bad states. The model links the liquidity premium to bank balance sheets and the supply of public liquidity, and it quantitatively explains a large share of the variation in the Treasury liquidity premium.

This framework changes how we should think about quantitative easing. QE is often discussed as a policy that lowers long-term rates by removing duration risk from the market. This paper isolates a different channel: QE changes the amount and composition of public liquidity available to the private sector. When the financial system is liquidity-stressed, more public liquidity can have large benefits. When banks are already well capitalized and liquidity is abundant, the marginal benefit is smaller.

The counterfactual results illustrate this distinction. QE1, implemented during the Global Financial Crisis, meaningfully improved output in the model through the liquidity insurance channel. Later QE rounds had much smaller effects through this channel because bank balance sheets and public liquidity conditions were different. The same policy tool can therefore have very different effects depending on the state of the financial system.

The COVID episode highlights the trade-off. A pandemic shock was not primarily a bank liquidity shock. It was closer to a real shock to production and capital values. Expanding public liquidity in that environment can support lending but may also increase banks' exposure to real shocks by encouraging more balance sheet expansion. The policy can reduce one kind of fragility while increasing another.

The takeaway is that safe government debt is part of the financial safety system, but more safety assets are not always unambiguously better. Public liquidity is valuable because it helps banks survive funding stress. Yet it also changes the size and structure of the banking sector. The right amount of public liquidity depends on the shock the economy faces and the condition of bank balance sheets.

This is why financial policy cannot be evaluated by labels alone. "QE," "liquidity support," or "safe asset supply" do not have fixed effects. Their consequences depend on whether the economy needs liquidity insurance, whether banks are fragile, and whether the main threat comes from funding runs or from real economic losses.