S9 Ep50: Tariffs, Uncertainty, and the Exchange Rate

Textbook economics says a tariff should strengthen a country's currency. Since the start of 2025, as US tariffs rose ... and the dollar fell.

In the first of four episodes of Voxtalks based on papers presented at the second Economic Policy: Papers on European and Global Issues conference, Alfonso Merendino (Bocconi University) and Tommaso Monacelli (Bocconi University, CEPR) tell Tim Phillips what they found when they looked for reasons. Their conclusion: for tariffs, it's not size, it is how permanent people expect it to be. They call this structural trade policy uncertainty.

When that uncertainty is low, a tariff behaves exactly as the textbook says. When it's high, the same tariff can weaken the currency, shrink output and pull down inflation instead.

The research behind this episode:

Merendino, Alfonso, and Tommaso Monacelli. 2026. "Tariffs, Uncertainty, and the Exchange Rate." Conference draft, presented at the 2nd Economic Policy: Papers on European and Global Issues Conference, Venice, 19-20 June 2026. Forthcoming in Economic Policy.

To cite this episode:

Phillips, Tim, Tommaso Monacelli, and Alfonso Merendino. 2026. "Tariffs, Uncertainty, and the Exchange Rate." VoxTalks Economics (podcast).

About the guests

Tommaso Monacelli is Professor of Economics at Bocconi University and a Research Fellow of IGIER Bocconi and CEPR. His research spans international macroeconomics, monetary policy and the business cycle, with recent work on tariffs and monetary policy, supply chain uncertainty and inflation, and heterogeneous bank models of monetary transmission. He is co-editor of the Journal of International Economics and was managing co-editor of Economic Policy from 2016 to 2021.

Alfonso Merendino is a PhD student in Economics at Yale University and a Research Fellow at the Social Economics Lab. He recently completed a research placement in macroeconomic modelling at the European Central Bank, and holds a Bachelor's and Master's degree in Economics from Bocconi University, where this paper was written.

Research cited in this episode

Structural trade-policy uncertainty (S-TPU). The paper's central measure, capturing uncertainty not about the size of a tariff but about how persistent the trade-policy regime behind it will be. Merendino and Monacelli split observed US tariff rates from 1990 to 2025 into a persistent component and a short-lived transitory one, using a state-space model with separate volatility for each, and define S-TPU as the volatility of the persistent component.

The 2017 US withdrawal from the Trans-Pacific Partnership. The authors' example of a pure S-TPU shock. The withdrawal changed no tariff rate on impact, but it reshuffled expectations about the durability of US trade policy, and their index of structural uncertainty spikes at this point.

"Liberation Day" tariffs, April 2025. The sweeping tariff package announced by the Trump administration on 2 April 2025. The paper treats this, alongside the 2018 Section 301 tariffs on China, as one of two clearly identified tariff shocks used to anchor its statistical model.

Aggregate trade-policy uncertainty index. Caldara, Dario, Matteo Iacoviello, Patrick Molligo, Andrea Prestipino, and Andrea Raffo. 2020. "The Economic Effects of Trade Policy Uncertainty." Journal of Monetary Economics 109: 38-59. This newspaper-based index of trade-policy uncertainty mixes announcement noise with genuine regime change; Merendino and Monacelli show that conditioning on it, rather than on their narrower S-TPU measure, erases the state-dependent pattern they document.

Narrative-dominance identification. The technique the authors use to isolate tariff shocks in their statistical model, adapted from Juan Antolín-Díaz and Juan F. Rubio-Ramírez. 2018. "Narrative Sign Restrictions for SVARs." American Economic Review 108 (10). Rather than imposing a full statistical model, the method anchors identification to a small number of clearly documented policy events, such as the 2018 and 2025 tariff rounds, and lets everything else, including the sign of the exchange-rate response, be estimated freely from the data.

More VoxTalks Economics episodes

The second Economic Policy: Papers on European and Global Issues conference follows the first, held in Paris in December 2025. Three earlier VoxTalks Economics episodes from that Paris conference asked what comes next for Ukraine's economy.

What's next for Ukraine: Investment, in which Yuriy Gorodnichenko and Maurice Obstfeld argue that forgiving Ukraine's war debt, rather than treating it as an obstacle, is essential to attracting the $40 billion a year that reconstruction needs.

What's next for Ukraine: Reconstruction, in which Edward Glaeser, Martina Kirchberger, and Andrii Parkhomenko argue that postwar Tokyo, not Warsaw or Berlin, is the right model for rebuilding Ukraine's cities.

What's next for Ukraine: The labour market, in which Giacomo Anastasia documents the surprising resilience of Ukraine's wartime labour market.

Related reading on VoxEU

Tariffs and US dollar depreciations: Not so surprising after all, a VoxEU column in which Giancarlo Corsetti, Simon Lloyd, and Daniel Ostry argue that the dollar's fall after Liberation Day is explained by foreign retaliation, a different mechanism from the persistence channel that Merendino and Monacelli identify.

Tariffs, the dollar, and equities: High-frequency evidence from the Liberation Day announcement, in which Jonathan Hartley and Alessandro Rebucci show that the dollar depreciated on impact on 2 April 2025, against the standard prediction, and trace this to foreign investors rebalancing away from US equities.