President Trump has proposed steel and aluminum tariffs, citing U.S. national security interests. Some experts argue that his plan could provoke retaliation from countries like China, or even a trade war.

The European Union has navigated a thicket of external and internal crises in recent years, including mass migration and Brexit. What are the union’s core institutions, and what roles do they play?

The separation of powers has spawned a great deal of debate over the roles of the president and Congress in foreign affairs, as well as over the limits on their respective authorities, explains this …