When Donald Trump became U.S. president in 2017, he promised an “America first” foreign policy of retrenchment. Starting with a flurry of executive orders, he set about undoing the foreign policy decisions of the Obama administration and undermining 70 years of cooperation with NATO allies. Who was there to stop him? Republicans controlled both houses of Congress during the first two years of the Trump presidency; the courts rarely step in when the other branches fight over control; and the American people tend to punish presidents only when they incur major losses in war. 

Trump’s agenda strayed from the norm, but his use of executive power did not. Presidents have dominated U.S. foreign policy decision-making since well before Trump. In fact, structural changes began to warp the separation of powers, allowing presidents tremendous leeway, more than 75 years ago. At first, those changes were difficult to enact: all three branches had to deny Congress the coequal status that the Constitution clearly confers on it. Congress made many efforts to guard the power it enjoyed during the first 150 years of the republic, but the altered relationship eventually became routine. By the twenty-first century, the branches had firmly established a new relationship: executives prosecute wars unilaterally, Congress provides little more than a fig-leaf of authorization (if any at all), and the courts rarely interfere. An accountable presidency attuned to the interests of the American people requires a legislature capable of restricting executive independence—and voters who insist on it. 

Abandoning Constraint 

President George Washington never engaged in a military operation without prior congressional approval. In 1793, he proclaimed U.S. neutrality in the French Revolutionary Wars and ran up against principled resistance: James Madison argued that by declaring a state of peace, Washington had encroached on Congress’s power to declare war. The modern reader might wonder how, then, U.S. presidents since Harry Truman have managed to initiate full-scale wars with limited, if any, input from Congress. 

The norm did not change right away or all at once. During his own presidency, Madison refrained from preparing for the War of 1812 until Congress had passed a declaration of war. James Polk appealed to Congress for funds and troops in order to prosecute the Mexican-American War. Congress was so powerful in 1898 that it all but forced William McKinley to start the Spanish-American War. Woodrow Wilson and Franklin Roosevelt each tried to get the United States into World War I and World War II respectively, but in both cases, Congress refused. It reconsidered its position only in response to the shocks of the sinking of the Lusitania and the attack on Pearl Harbor. 

The attack on Pearl Harbor was, in fact, the catalyst not only for pulling the United States into World War II but also for fundamentally altering the separation of powers. Some members of Congress, especially in the Senate, had viewed the United States as a continental fortress, untouchable by the fighting in Europe or in the Pacific. Pearl Harbor shattered this worldview by proving that a resourceful enemy could harm the United States. Congress declared war and provided FDR with all of the appropriations he desired, giving the following instructions: “the President is hereby authorized and directed to employ the entire naval and military forces of the United States and the resources of the Government to carry on war against the Imperial Government of Japan, and to bring the conflict to a successful termination, all of the resources of the country are hereby pledged by the Congress of the United States.” 

Although the declaration appears to confer a great deal of power on the president, it also implies significant constraint. Only Congress could authorize the president to start a war, only Congress could permit the president to spill blood and use treasure, and Congress defined the enemy— “the Imperial Government of Japan,” as opposed to the Japanese nation or any particular people. The president then used this declaration and those that followed against other World War II enemies to assert broad powers in carrying out the war. Members of Congress tried to avoid questioning the president’s decisions, and the public largely supported them, showing unity even in the darkest days of the war. 

Trump’s agenda strayed from the norm, but his use of executive power did not.

Such unity was normal in an existential crisis such as World War II, and the constitutional structure could accommodate this consolidation of immense power in the hands of the president. But once the Allies declared victory, first in Europe and later in the Pacific, Congress should have reasserted its coequal status and reclaimed its powers. Such had been the course after every prior conflict—so much so, in fact, that at the end of World War I, the Senate refused to pass Wilson’s League of Nations treaty, citing the concern that Congress, and not an international body, should retain exclusive control over when and where the United States went to war. 

After World War II, however, those concerns apparently evaporated or were superseded. The Senate quickly and easily passed the UN and the NATO treaties—both of which gave other countries the ability to force the United States into conflict. Amid the wreckage of the war, from which the United States had emerged a superpower, members of the Senate did not see or did not care to acknowledge how much control they were ceding to international institutions, as they worried more perhaps about stopping another great-power war than about protecting their constitutional authority.

The provisions of those treaties were quickly put to the test: in 1950, the UN Security Council issued resolutions calling for member states to defend South Korea against North Korean aggression. Truman, unlike his predecessors, found himself in a position to make the decision without asking permission from Congress. With a large standing army at his disposal and the Soviet enemy at his back, Truman felt compelled to act, and he acted impulsively. 

U.S. President Barack Obama's State of the Union address in Washington, D.C., January 2011
U.S. President Barack Obama's State of the Union address in Washington, D.C., January 2011
Jim Young / Reuters

The Korean War demonstrates how important congressional checks on presidential action can be. Had Truman needed to appeal to Congress, he would have had to prove the legitimacy of the operation to the American people, and Congress could have used oversight to ensure accountability throughout the operation. Furthermore, Americans could hold members of Congress accountable when the war took a bad turn (as most wars do). But Truman acted on his own, leaving Congress with limited ability to constrain him. For if Congress does not assert control at the beginning of a war, it can use its powers only to draw down troops in dire circumstances. After all, once the military is in the field, members of Congress look unpatriotic if they fail to provide fighting men and women with the equipment they need to succeed. 

Such was the case in Vietnam. Congress never declared war there—if it had, it might then have exercised some oversight over the conflict. But in 1964, President Lyndon Johnson pressed Congress to pass the Gulf of Tonkin Resolution, which authorized what he fancifully promised would be a limited engagement. With that legislation, Congress now found itself allowing the undeclared war in Vietnam to escalate at the president’s discretion rather than holding the executive accountable. After nearly a decade of fighting, the deaths of tens of thousands of soldiers, and no victory in sight, Congress attempted to reassert itself in 1973, passing the War Powers Resolution (WPR) over President Richard Nixon’s veto. 

On its face, the WPR appeared to require the president to consult the legislature before and throughout foreign conflicts. But what looked like a reassertion of the separation of powers instead came to function as a form of permission. The WPR clearly stipulated that in the absence of an attack against the United States, a president could not commit American troops without first securing a declaration of war or a statutory authorization from Congress. The WPR went on, however, to say that the president might initiate operations unilaterally so long as he concluded them within 60 days and drew down troops within another 30 days. Presidents have used this language to justify small-scale operations ever since, including some that have grown larger and costlier than advertised, such as those in Kosovo and Libya. 

Politics as Usual

When President George W. Bush took office in 2001, he inherited a powerful executive branch checked by a weak legislature in the realm of foreign affairs. Bush gave presidential power a shot of steroids following the terrorist attacks on 9/11, and his successors expanded presidential power still further. Twenty-first century presidents can now cite decades of precedent for initiating military operations without consulting Congress. They can justify fighting stateless actors in open-ended conflicts that require quick, decisive, and covert action, leaving little time for devising clear policy objectives let alone a feasible grand strategy. 

Worse, presidents prosecute these forever wars with authorizations from Congress that look too much like the Gulf of Tonkin Resolution and too little like the declaration of war in World War II. In 2001, Congress passed an Authorization for Use of Military Force, which gave the president the power to pursue anyone connected with the 9/11 attacks. In 2002, Congress passed an AUMF authorizing the war in Iraq, and the last two presidents have repurposed this document to provide legal justification for all sorts of operations, including the airstrike that killed Iranian Major General Qasem Soleimani in January 2020. 

George Washington never engaged in a military operation without congressional approval.

For decades, presidents have asked for or wrested foreign policy control out of Congress’s hands, and Congress now has little incentive to recover it. A president’s party can sometimes pay a price for serious missteps, as the Republicans did in the 2006 midterm election when the war in Iraq had reached one of its lowest points. But for the most part, voters do not hold Congress accountable for presidential failures in foreign policy, nor do they punish Congress for failing to hold presidents accountable. Congress and the people have accepted presidential unilateralism.

Presidents can and do use UN Security Council resolutions and NATO authorizations to bypass Congress when they wish to take military action. Presidents can and do use the 2001 and 2002 AUMFs much the way that Johnson used the Gulf of Tonkin Resolution: to render Congress powerless to stop the executive. A return to the intended separation of powers might not put an end to all unnecessary or poorly executed wars. But substantive congressional oversight would provide transparency so that the American people might know when wars go awry rather than waiting ten years to discover, say, that not one but two administrations had failed to manage the war in Afghanistan effectively. 

At the conclusion of the 2020 presidential election, many are looking to President-elect Joe Biden to return the United States to “politics as usual.” In the realm of foreign policy, however, and especially in military affairs, Trump’s unilateralism already was politics as usual. The pattern of executive unilateralism in foreign policy will not break under a different administration. It will only break when a reinvigorated Congress determines that it must restrict presidential action and hold presidents accountable.

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