President Donald Trump holds up a chart while speaking during a trade announcement event at the White House on April 2, 2025. | Chip Somodevilla/Getty ImagesPresident Donald Trump has described the ongoing Supreme Court case over the legality of his use of emergency powers to impose tariffs on more than 100 countries as a matter of “literally, LIFE OR DEATH for our Country.” Certainly the case, in which oral arguments were heard at the Court on Wednesday, has profound implications for executive power and, as my colleague Ian Millhiser explained earlier this week, will be a key indicator of the court’s willingness to rein in the administration. Based on the hostile questions from the conservative justices on Wednesday, the court appears likely to rule against Trump — a potentially serious blow to the administration, and not only its economic policies. Trump is a self-described “tariff man,” and tariffs are rivaled perhaps only by mass deportations as the signature policy of his second term. Trump loves tariffs in large part for their traditional function: protecting US industries from foreign competition and raising government revenue, and is unpersuaded by the arguments of most economists that US consumers will ultimately bear the costs of these measures. But less noticed is the degree to which tariffs have also become the centerpiece of Trump’s foreign and security policy. It sometimes seems as if there’s hardly a problem in the world that Trump doesn’t think can be solved with more tariffs.Just this week, for instance, the Financial Times reported that US officials have been waging a campaign of intimidation to block a new treaty on shipping emissions, threatening new tariffs against countries that support the agreement. Trump has used tariffs to address broad geopolitical challenges, including levying them against countries like India that buy the oil Russia uses to fund its war in Ukraine. And he has used them for his personal grievances, like threatening a 50 percent tariff on Brazil over the prosecution of former President Jair Bolsonaro, a Trump ally. Trump has also used tariff threats to assert dominance over smaller countries, like Colombia, which attracted his ire in the first weeks of his term by refusing to accept deportation flights on military planes. And he has used them against some of America’s largest trading partners, like the tariffs he slapped on China, Mexico, and Canada over their alleged failure to stop the flow of fentanyl into the US. Tariffs have even been part of Trump’s quest for a Nobel Peace Prize: Cambodia and Thailand were told they could not negotiate a tariff relief deal until they pulled back from a deadly border dispute. In some respects, Trump is not acting out of character here. The political scientists Henry Farrell and Abraham Newman have coined the term “weaponized interdependence” to describe how powerful states like the US have leveraged their position within the global economy to accomplish strategic goals. The difference is that previous administrations more typically used sanctions — legal measures to prevent economic transactions with certain countries or entities — rather than tariffs: duties imposed on traded goods as they cross borders. “Using tariffs for the purposes that they have been used by this administration is frankly weird,” Farrell told me. “It doesn’t make very much sense.”The US overreliance on sanctions — about a third of the countries in the world are under some form of American sanctions — has its own drawbacks. But their advantage is that, at least in principle, the costs to the sanctioner are minimal. By relying on tariffs, the Trump administration is forcing US importers and consumers to bear at least some of the costs for punishing adversaries. Much of American economic statecraft in recent years has operated under the same principle: to take advantage of the “chokepoints” in the global economy that are controlled by the United States. For instance, most international transactions are carried out in dollars, which gives the US enormous leverage to cut targets off from the global financial system. Many countries desperately want advanced semiconductors, a sector America and its allies happen to dominate. Trump, on the other hand, is essentially using America’s status as a destination for countries’ exports as an economic weapon. This is the source of some leverage, but it’s not exactly a chokepoint. The US accounts for 25 percent of global GDP, but only 13 percent of imports. So Trump can make countries feel pain in the short run, but in the long run, he’s going to encourage them to find new customers. “When you’re using import tariffs as a weapon of economic warfare, you’re attempting to weaponize what is a relative weakness of the US economy,” said Eddie Fishman, a Columbia University professor who helped craft US sanctions policy as a State Department staffer in the Obama administration.The nature of tariffs also limits the targets on which they can be used. Tariffs won’t do much good against Russia, for instance. Trade between the US and Russia is almost nonexistent. And a country like China has the capacity to retaliate, as it has demonstrated with its restrictions on rare earths exports. All of this means that the tariff weapon tends to be more effective when wielded against US allies rather than adversaries. So why is Trump doing this? The president did use sanctions aggressively in his first term, and has in some circumstances in his second, but he also seems to dislike them as a tool and has expressed concern that they undermine global confidence in the dollar as a reserve currency. Ever a political child of the 1980s, Trump’s views may also be shaped by how the US wielded tariffs against Japan during that country’s economic boom. He also appears to believe that tariffs are simply beneficial to the US economy anyway, so he might just see their geopolitical advantage as an added bonus. (Trump officials sometimes appear confused about the difference between the two economic tools. White House spokesperson Karoline Leavitt, for instance, described the Russian oil-related tariffs on India as “sanctions,” which caused an uproar in New Delhi.)Trump’s tariff diplomacy has racked up a few wins, but they have tended to be against smaller countries like Colombia and Thailand or to have only extracted relatively minor concessions, like the measures that Canada and Mexico have announced on fentanyl. India does appear to be finally curbing its purchases of Russian oil, though the sanctions the US also announced on Russian oil giants Rosneft and Lukoil may have more to do with that. The tariffs’ longer-term consequences are less certain. The IMF has warned that tariffs are likely to be a drag on global growth. Countries also now have a greater incentive to diversify away from the US market for their exports. Fishman also worries that “it will be hard to remove the tariffs for future US administrations, even if doing so is wise from an economic standpoint, because we’re increasingly dependent on tariff revenue to fund the government.” This has been shown most acutely in recent days by the White House dipping into tariff revenue to fund programs during the government shutdown.Wednesday’s Supreme Court session suggests the Trump administration may need to rethink its strategy. White House officials say they are devising legal strategies to continue imposing tariffs without the emergency powers that are being challenged in this case. Given how many uses they have found for this tool, it seems unlikely they will part with it without a fight.