NBER Working Papers · 2026 · Ricardo J. Caballero
中文摘要
即使主权国家仍具有偿付能力，安全公共债务也可能成为总需求的拖累。其安全性需要展期支持、做市和资产负债表容量。随着这些资源日益稀缺，创设安全国债债权的边际成本随之上升。由此产生的财政调整会减少总支出，并最终可能超过增加安全资产供给所带来的扩张效应。此时，债务对总需求的稳态贡献达到峰值，均衡安全利率也在同一债务存量水平上达到最大值。超过这一点后，尽管债务仍然安全，进一步发行债务仍会降低总需求和安全利率。在实证分析中，我将现金—国债溢价和实际久期溢价，与额外私人供给如何对未偿国债存量重新定价的估计结合起来。过去十年间，基准边际成本增加了一倍多，从2015年第一季度的约80个基点升至2026年第一季度的187个基点。以330个基点作为利率等价财富收益的基准，安全债务边际——即该收益与边际成本之差——从约250个基点降至143个基点。按照美国国会预算办公室（CBO）2026年的借款速度，剩余的安全债务边际将在一年内缩减约18个基点；随着债务相对于金融承载能力继续上升，其进一步缩减的速度还会加快。
Abstract
Safe public debt can become a drag on aggregate demand even while the sovereign remains solvent. Its safety requires rollover support, market-making, and balance-sheet capacity. As these resources become scarce, the marginal cost of producing safe Treasury claims rises. The resulting fiscal adjustment reduces aggregate expenditure and can eventually outweigh the expansionary effect of increasing the supply of safe assets. Debt’s stationary contribution to aggregate demand then peaks, and the equilibrium safe rate reaches its maximum at the same debt stock. Beyond this point, further issuance lowers aggregate demand and the safe rate even though the debt remains safe. Empirically, I combine cash- Treasury and real-duration premia with estimates of how additional private supply reprices the outstanding Treasury stock. Over the past decade, the benchmark marginal cost more than doubled, rising from about 80 basis points in 2015Q1 to 187 basis points in 2026Q1. Using a 330-basis-point benchmark for the rate-equivalent wealth benefit, the safe-debt margin—the difference between this benefit and marginal cost—fell from about 250 to 143 basis points. At the CBO’s 2026 borrowing pace, the remaining safe-debt margin shrinks by about 18 basis points in one year, with further erosion accelerating as debt rises relative to financial capacity.