This week, Donald Trump imposed new tariffs on 60 countries, including the UK, EU and Canada, escalating a trade war that has defined his second term. The move demonstrates the President’s persistence in attempting to reshape American foreign policy, despite numerous previous setbacks. But why are his tariffs proving so hard to implement legally?

In February, the Supreme Court ruled that Trump does not have the legal authority to impose tariffs under the International Emergency Economic Powers Act (IEEPA). This is an obscure 1977 law that allows the president to regulate “importation or exportation” during national emergencies. In addition to invalidating tariffs that had been imposed on China, Mexico, and Canada, the Court’s decision wiped out the “reciprocal” tariffs that Trump had imposed on more than 180 countries. To salvage something like these tariffs, he invoked yet another legislative authority: Section 122 of the 1974 Trade Act. This allows the president to impose 15% tariffs for up to 150 days without congressional authorization, with an extension possible if needed.

These temporary Section 122 tariffs expired yesterday, and the new measures were subsequently invoked. Trump’s claimed tariff authority has jumped from the IEEPA to Section 122 to Section 301 of the Trade Act of 1974. The earlier tariffs were justified by the claim of a national emergency caused by US trade deficits, while the new measures have been put in place by the alleged need to combat forced labor. Countries that have taken steps to ban forced labor from their supply chains, such as the UK, are set to pay the lower rate of 10%, while others like Norway that have allegedly failed to do so will pay the full 12.5% penalty.

If a policy remains the same, but the way in which it is publicly justified changes, then clearly there is another underlying reason for its implementation. Trump’s unstated justification for maintaining these tariffs is the idea that the US should adopt a global or baseline levy on all trading partners that can be lowered in multilateral negotiations.

As a bargaining chip to begin trade negotiations, a baseline tariff makes perfect sense in theory, but it directly contradicts the theory of liberal internationalism. This utopian theory was identified by Britain’s William Gladstone and America’s Woodrow Wilson, which unfortunately became the basis for the economic and military arrangements of the post-1945 US alliance system.

According to the theory of liberal internationalism, wars are often caused by economic protectionism but carried out by national militaries. Achieving world peace therefore requires stripping states of the power to protect their producers and defend themselves unilaterally. All countries should renounce their economic sovereignty by permanently abandoning the use of tariffs and joining a regional or global free-trade order. At the same time, war can be avoided forever if states renounce their military sovereignty, delegating power to a quasi-world government such as the United Nations, or lesser regional alliances such as Nato or the EU.

Compared to this utopian ideal of liberal internationalism, Trump-style economic nationalism is more grounded in common sense and represents a long-overdue return to tradition. It was an accident of history that liberal internationalism was adopted by American leaders after the Second World War. All other great powers had been weakened or destroyed, and the so-called “liberal international order” and the zone of American military-commercial hegemony conveniently overlapped. In recent years, the rise of China and the revisionism of powers including Russia and Iran have resulted in the costs of American liberal internationalism outweighing the benefits to US citizens. In this sense, a retreat from global free trade and unilateral world policing was inevitable, even if Trump had never been elected.

The problem is that Trump wants to move the US back to its historic system in which protectionism was the norm, with limited, specific exceptions. But the President must work within an inherited structure of US and international trade law which assumes that free trade is the norm and any deviations must be justified. This is often done by complex investigations designed to slow down protectionist actions.

Until Congress radically revises obsolete trade laws to fit the new realities of our multipolar, neo-mercantilist world, American presidents will be forced to conceal their actual goals. Instead, like Trump, they will have to invoke obscure, long-dormant trade measures designed by 20th-century Wilsonian ideologues to promote a global free market in a post-national order that never properly existed and never can exist.