Trade has taken center stage during the administration of President Donald J. Trump, who has set out to renegotiate long-standing deals and challenge a system that he says has been unfair to American workers. While the United States has long led the charge for global trade liberalization—in the belief that open, rules-based markets increase prosperity and expand Washington’s influence—rising inequality has led to growing skepticism about this model within both major parties. At the same time, U.S. policymakers have struggled with how to confront an increasingly assertive China, which they say is relying on unfair trade practices that include export subsidies and intellectual property theft.

The Barack Obama administration tried to step up the enforcement of trade rules, bringing cases against Beijing at the World Trade Organization (WTO). But Trump has dramatically upped the ante, launching a trade war with China, imposing tariffs on U.S. allies, and signaling a more fundamental disruption of the global trading system by undermining the WTO’s dispute settlement mechanism and threatening to withdraw from the body altogether.

Many across the political spectrum warn that Trump’s trade war is isolating Washington, hurting the U.S. and global economy, and failing to change China’s behavior. The issue divides the Democratic candidates, many of whom have long complained that trade deals benefit multinational corporations at the expense of American workers and the environment, even if they disagree with Trump’s go-it-alone approach. Meanwhile, Trump’s unprecedented tactics are pushing the limits of what Congress—which has the constitutional power to regulate foreign commerce—has authorized, which some experts say could lead to pushback from legislators.