12/16エントリで紹介した研究について、IMFが著者の一人であるサージェントにインタビューしている(H/T Mostly Economics)。

IMF Survey: Professor Sargent, could you please explain the role debt limits have played in the economic history of the U.S.?

Sargent: Based on the evidence that my friend George Hall and I have assembled, the answer is different before 1917 and after 1939.

Before 1917, there was not an aggregate debt limit. Instead, interestingly, there was a debt limit bond by bond. Congress designed every bond and put a limit on the amount that could be issued. And those limits were taken seriously. They seem to have provided information about what upper bound on what future debt would be, except during wars.

After 1939, an aggregate debt limit was created for the first time. It restricts the par value of the total amount of debt. If you adjust for inflation, in real value, the government debt limit was constant until a little after 1980. It actually went down after 1945. In real terms, the value of debt relative to GDP went down even more. After 1983, nominal debt limits rose and more than inflation except in the Clinton administration. So, as I said, the answer seems to differ substantially after 1939 and before 1917.

IMF Survey: And what was the reason for moving from this bond-by-bond approach to the aggregate limit?

Sargent: Good question. The U.S. Secretary of the Treasury, Andrew Mellon, gave his reasons. After World War I, the federal government had big debts. These debts were in discrete issues of bond of particular maturities. They were issued in big lumps with “echo effects”: lumpy debt service events; potential liquidity and roll-over risks. In the 1920s, the U.S. ran a primary surplus, but not big enough to service all the debt that would come due. So when those big bonds matured, Mellon knew that he was going to have to ask Congress for authority to issue new bonds. He foresaw those “echo effects”. So he asked Congress for authority and flexibility to smooth those things over time. Congress assented. Mellon wanted to manage the debt in ways that would increase the liquidity and allow him freedom basically to be a good portfolio manager.
It is interesting why Congress assented to Mellon’s request while it had denied such requests from earlier Secretaries of the Treasury. You have to know more about the politics of the times than I do to answer that question. The Republicans had big majorities in Congress in the 1920s and they mostly trusted Mellon. Congress evidently thought Mellon’s was a reasonable request and at that time he was respected a lot.

IMF Survey: What is the most interesting thing you have learned from your work?

Sargent: To me, one of the most fascinating things is how the U.S. Congress and Treasury recognized and managed rollover risks and interest rate risks; and how they thought about the sources of the fundamentals that drove interest rate risk, some under the government’s control, some not. Many of their discussions and decision seem very wise and modern. The government did various things about rescheduling and issuing callable debt and exercising call options. It was quite a sophisticated operation, done 150 years ago. We are trying to understand: (1) were those good things to do; and (2) what motivated those decisions.

IMF Survey: What’s next for your research?

Sargent: Debt limits are just a part of what we are doing. We are digging deeper and trying to find interesting stories behind individual episodes. Then, we hope to tell some convincing stories—and supplement them with sensible analysis.