Article I of the Constitution enumerates several of Congress’s foreign affairs powers, including those to “regulate commerce with foreign nations,” “declare war,” “raise and support armies,” “provide and maintain a navy,” and “make rules for the government and regulation of the land and naval forces.” The Constitution also makes two of the president’s foreign affairs powers—making treaties and appointing diplomats—dependent on Senate approval.

Beyond these, Congress has general powers—to “lay and collect taxes,” to draw money from the Treasury, and to “make all laws which shall be necessary and proper”—that, collectively, allow legislators to influence nearly all manner of foreign policy issues. For example, the 114th Congress (2015–2017) passed laws on topics ranging from electronic surveillance to North Korea sanctions to border security to wildlife trafficking. In one noteworthy instance, lawmakers overrode President Barack Obama’s veto to enact a law allowing victims of international terrorist attacks to sue foreign governments.

Congress also plays an oversight role. The annual appropriations process allows congressional committees to review in detail the budgets and programs of the vast military and diplomatic bureaucracies. Lawmakers must sign off on more than a trillion dollars in federal spending every year, of which more than half is allocated to defense and international affairs. Lawmakers may also stipulate how that money is to be spent. For instance, Congress repeatedly barred the Obama administration from using funds to transfer detainees out of the military prison at Guantanamo Bay.

Congress has broad authority to conduct investigations into particular foreign policy or national security concerns. High-profile inquiries in recent years have centered on the 9/11 attacks, the Central Intelligence Agency’s detention and interrogation programs, and the 2012 attack on U.S. diplomatic facilities in Benghazi, Libya.

Furthermore, Congress has the power to create, eliminate, or restructure executive branch agencies, which it has often done after major conflicts or crises. In the wake of World War II, Congress passed the National Security Act of 1947, which established the CIA and National Security Council. Following the 9/11 attacks, Congress created the Department of Homeland Security.