The Trump administration on May 24 announced an emergency declaration to sell billions of dollars worth of arms to Saudi Arabia without congressional approval.

This comes just a month after Congress passed legislation demanding the halt of U.S. aid for the Saudi-led intervention in Yemen against Houthi rebels loosely aligned with Iran.

President Trump vetoed the measure, but reports cast this confrontation as a major challenge to executive war powers.

How Congress responds to the emergency arms sales may signal whether the Yemen vote represents an isolated event or the first salvo in a campaign to limit the president’s foreign policy powers.

My current research examines individuals who once saw Congress as a check on presidential interventionism abroad. After the Vietnam War, legislators like Frank Church and Dick Clark wanted to rethink national security structures and priorities. Their foreign policy revolt inspired the War Powers Act of 1973, the law Congress used to express its disapproval of Saudi aid.

Revisiting this history – and the difficulty legislators have had reigning in presidential power – provides context for analyzing recent events.

The birth of the imperial presidency

The Constitution’s separation of powers is at the heart of the current conflict between Trump and Congress. Separation of powers means each branch of government has distinct but overlapping duties, making negotiation and compromise necessary in forging policies.

In terms of foreign affairs, the president manages diplomacy while the Congress funds it, regulates commerce and approves treaties.

But when it comes to war powers, the Constitution is vague.

Congress – with two bodies, 535 members and a tendency toward deliberation – has the sole right “To declare war, [and] grant letters of marque and reprisal,” the latter being 18th century methods of limited warfare.

The more nimble presidency directs and deploys the armed forces as commander-in-chief.

The terse Constitution says little about how the two bodies should manage these divided responsibilities. Presidential prerogative generally won the day as U.S. power grew in the 19th century, though not without periodic dissent. Most of the 200 plus foreign military deployments in U.S. history – which include only five declared wars – lacked advanced congressional authorization.

This history of executive-legislative jockeying is largely absent from discussions of foreign policy due to the politics of the early Cold War. As communist paranoia and the threat of nuclear weapons stoked domestic unease, Congress empowered the executive branch.

Congress had earlier given up control of key trade and economic powers during the Roosevelt era. Now it embraced long-taboo collective security treaties and conceded to unilateral military deployments and covert operations championed by the White House.

Most legislators agreed the United States had a global mission and the president was best positioned to guide it. “Politics,” as the motto paraphrasing Republican Sen. Arthur Vandenberg went, “must stop at the water’s edge.”

Disagreements over emphasis or direction usually occurred in private meetings or at the edges of budget requests. This expanded executive authority gave rise to what some scholars call the “imperial presidency,” a term coined by Arthur Schlesinger Jr. in 1973.

The congressional revolt of the 1970s

Only when the Vietnam War shattered this consensus did Congress embrace new structures to constrain presidential power. A generation of politicians that historian Robert David Johnson calls “the new internationalists” used anger over the unpopular war to champion an alternative vision of U.S. foreign policy.

These leaders rejected strict anti-communism and militarist interventions in favor of diplomacy, cooperative aid and reduced defense spending. They also sought to place legislative constraints on executive privilege.

This revolt used the traditional powers of Congress. The Church Committee investigated and publicized covert operations in 1975. The Clark Amendment to the 1976 Arms Export Control Act forbade distribution of aid to anti-communists in Angola.

There were also new laws. The 1974 Hughes-Ryan Amendment to the Foreign Assistance Act requires that the executive branch disclose covert operations to key congressional committees.

Even more bold was the War Powers Act, which passed over Richard Nixon’s veto in 1973. This joint resolution requires Congress to approve any deployment of American military forces within 60 days.

Though the War Powers Act formalized congressional authority and tried to limit when presidents could use unilateral force, it could not reverse over a century of accepted practice. The act yields to the president the ability to deploy troops proactively and specifically excludes covert operations from the approval process. Effectively, Congress recognized the imperial presidency even as it sought to limit it.

Reluctantly supported by the new internationalists, the act was a vaguely worded compromise that reflected a hard reality. The centrist critics who passed the law chafed at Vietnam, Watergate and the Nixon administration’s secretive handling of foreign affairs, but they could not fully abandon the Cold War or the presidential authority used to fight it.

What comes next

Even this qualified moment of congressional reassertion proved short-lived. Ronald Reagan’s revival of anti-communist rhetoric mobilized voters against the new internationalists, weakening the appetite for congressional assertiveness.

The Cold War mission still championed by many legislators transitioned to the militarized humanitarianism of the 1990s – as in Somalia and Haiti. Still later came anti-terrorism after 9/11. The responsive, flexible power of the presidency seemed best suited to handle these new political realities.

Indeed, Congress has been loath to use its war powers since the 1970s. It has provided blanket authorizations for military operations across the world. This famously occurred with 2001’s broadly defined Authorization for Use of Military Force that continues to legitimize interventions in Somalia and Yemen as part of the War on Terror.

Even when Congress has refused such authorizations – notably in Libya in 2011 – it has not effectively challenged presidential prerogative. Barack Obama sidestepped an irked Congress by claiming that supporting NATO in Libya did not constitute hostilities and therefore did not require legislative permission.

Indeed, it seems congressional acquiescence to the imperial presidency remains even in today’s divided Congress. Though championed by legislators with deep reservations about U.S. policy, the long-simmering Yemen issue only gained political traction due to President Trump’s missteps in the Middle East. His tepid public response to Jamal Khashoggi’s murder combined with his waffling on regional troop commitments, causing consternation among Republicans and centrist Democrats.

It’s no coincidence that the monthslong Yemen debate book-ended the Senate’s rebuke of Trump’s planned withdrawal of troops from Syria. Taken together, these votes signal that legislators are leery of Trump’s unpredictability and unprincipled rhetoric, but many still stand behind an interventionist foreign policy led by a powerful executive branch.

There is a minority associated with the Democratic Party who want to challenge this consensus. Bernie Sanders has been the most prominent voice urging a reevaluation of American foreign policy with a strong Congress as a key player.

Yet history shows how difficult it will be to seriously alter the dominant national mindset and the executive-legislative balance of power in foreign affairs. How Congress responds to the president’s ongoing efforts to aid Saudi Arabia – and how it uses its powers to limit unilateral executive actions more broadly – will prove whether it is truly reasserting its constitutional authority.

R. Joseph Parrott is affiliated with Westerville Progressive Alliance.