Five years into a once-unthinkable trade war with China, US Treasury Secretary Janet Yellen chose her words carefully on April 20. In a wide-ranging speech, she reversed the terms of US engagement with China, prioritizing national-security concerns over economic considerations. That formally ended a 40-year emphasis on economics and trade as the anchor to the world's most important bilateral relationship. Yellen's stance on security was almost confrontational: "We will not compromise on these concerns, even when they force trade-offs with our economic interests."

Yellen's view is very much in line with the strident anti-China sentiment that has now gripped the United States. The "new Washington consensus," as Financial Times columnist Edward Luce calls it, maintains that engagement was the original sin of the US-China relationship, because it gave China free rein to take advantage of America's deal-focused naiveté. China's accession to the World Trade Organization in 2001 gets top billing in this respect: the US opened its markets, but China purportedly broke its promise to become more like America. Engagement, according to this convoluted but widely accepted argument, opened the door to security risks and human-rights abuses. American officials are now determined to slam that door shut.

There is more to come. President Joe Biden is about to issue an executive order that will place restrictions on foreign direct investment (FDI) by US firms in certain "sensitive technologies" in China, such as artificial intelligence and quantum computing. The US rejects the Chinese allegation that these measures are aimed at stifling Chinese development. Like sanctions against the Chinese telecoms giant Huawei and those being considered against the social-media app TikTok, this one, too, is being justified under the amorphous guise of national security.

The US case rests not on hard evidence but on the presumption of nefarious intent tied to China's dual-purpose military-civilian fusion. Yet the US struggles with its own security fusion - namely, the fuzzy distinction between America's under-investment in innovation and the real and imagined threats of Chinese technology.

Significantly, Yellen's speech put both superpowers on the same page. At the Communist Party's 20th National Congress last October, Chinese President Xi Jinping's opening message also stressed national security. With both countries equally fearful of the security threat that each poses to the other, the shift from engagement to confrontation is mutual.

Yellen is entirely correct in framing this shift as a tradeoff. But she only hinted at the economic consequences of conflict. Quantifying these consequences is not simple. But the American public deserves to know what is at stake when its leaders rethink a vitally important economic relationship. Some fascinating new research goes a long way toward addressing this issue.

A just-published study by the International Monetary Fund (summarized in the April 2023 World Economic Outlook) takes a first stab at identifying the costs. IMF economists view the problem through the lens of "slowbalization": the reduction of cross-border flows of goods and capital, reflected in geostrategic strategies of "reshoring" (bringing offshore production back home) and what Yellen herself has called "friend-shoring" (shifting offshore production from adversaries to like-minded members of alliances).

Such actions result in "dual bloc" FDI fragmentation. The IMF estimates that the formation of a US bloc and a China bloc could reduce global output by as much as 2% over the longer term. As the world's largest economy, America will account for a significant share of foregone output.

European Central Bank President Christine Lagarde recently stressed a different channel through which an escalating US-China conflict could adversely affect economic performance. Drawing on research by ECB staff, she focuses on the higher costs and inflation resulting from supply-chain disruptions implied by conflict-driven FDI fragmentation. The ECB study concludes that geostrategic conflict could boost inflation by as much as 5% in the short run and around 1% over the longer term. Collateral effects on monetary policy and financial stability would follow.

Collectively, these model-based calculations of the costs of conflict imply a stagflationary combination of lower output and higher inflation - hardly a trivial consideration in today's fragile economic climate. And they dovetail with economic theory. Countries trade with others to reap the benefits of comparative advantage. Both inward and outward flows of foreign investment seek to achieve similar benefits, offering offshore efficiencies for multinational corporations that face higher costs in their home markets and attracting foreign capital to support domestic capacity expansion and job creation. Regardless of their different political systems and economic structures, this is true for both America and China. It follows that conflict will reduce these benefits.

Yet there is an important twist for the US: a chronic shortfall of domestic saving casts the economic consequences of conflict with China in a very different light. In 2022, net US saving - the depreciation-adjusted saving of households, businesses, and the government sector - fell to just 1.6% of national income, far below the longer-term 5.8% average from 1960 to 2020. Lacking in saving and wanting to invest and grow, the US takes full advantage of the dollar's "exorbitant privilege" as the world's dominant reserve currency and freely imports surplus saving from abroad, running a massive current-account and multilateral trade deficit to attract foreign capital.

As such, the economic interests of saving-short America are tightly aligned with its outsize imbalances of trade and capital flows. Barring a highly unlikely resurgence of domestic US saving, compromising those flows for any reason - say, security concerns over China - is not without meaningful economic and financial consequences. The research cited above suggests those consequences will take the form of slower economic growth, higher inflation, and possibly a weaker dollar.

This is hardly an ideal outcome for a US economy that is already at a precarious point in the business cycle. The tradeoff for national security should not be taken lightly. Nor should the US penchant to over-hype the security threat be accepted on blind faith.

From Project Syndicate