The return of unified Republican control of government for the first time in a decade thus far has failed to produce major legislation on a host of domestic policy priorities. However, the 115th Congress has notched some victories in foreign policy, most notably in leading the response to Russian interference in our democratic processes.

In a sharp rebuke to President Trump, Congress imposed new sanctions on Russia and barred the president from lifting or even easing them unilaterally. The overwhelming, veto-proof majorities backing the bill all but forced President Trump to sign it into law. However, in his signing statement Trump lashed out calling the bill “seriously flawed” and an unconstitutional encroachment on executive power.

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At least since the conclusion of World War II, Congress has consciously taken a back seat to the executive in foreign affairs. In unified government, partisan loyalties routinely stifle serious challenges to presidential prerogatives. More generally, most members of Congress often lack strong incentives to invest substantial time and energy in foreign policy. As such, Congress often rationally defers to the executive in the international sphere.

And yet, this status quo of presidential dominance is periodically punctuated by bursts of congressional reassertion. An oft-overlooked, but critically important trigger behind many cases of congressional pushback, including the contemporary one over Russia policy, is Congress’ investigative power.

President Trump is far from the first chief executive to dismiss a congressional inquest as nothing more than a politically motivated witch hunt. Even so, investigations excel at shining a light on alleged misconduct and bringing political pressure to bear on the White House.

In some cases, investigations encourage presidents to make concessions in the hopes of diffusing a controversy and moving it off of the front pages. In others, investigations spur an otherwise reluctant legislature – occasionally, even one controlled by the president’s partisan allies – to overcome its institutional inertia and check a wayward commander in chief.

During World War II, Harry Truman burst on to the national political stage as the head of a Senate committee investigating maladministration of the war effort on the home front. The Truman Committee shone a bright light on waste, fraud and inefficiencies in wartime procurement and forced President Roosevelt to make significant changes to the running of the war effort.

A quarter century later, Sen. William J. Fulbright (D-Ark.) took aim directly at the war conduct of both Presidents Johnson and Nixon through a years-long investigation alleging policy blunders and abuses. By shining a light on these failings, the Fulbright investigation helped lay the foundation for subsequent congressional efforts to repeal the Gulf of Tonkin Resolution, cut off funds for Nixon’s clandestine escalation of the war into Cambodia, and, ultimately, to end the war itself.

After Vietnam, investigators broadened their focus to another instrument of executive control over foreign policy: the intelligence services and covert operations. The Church Committee’s investigation prompted President Ford, in an effort to preempt more extreme congressional action, to sign an executive order reorganizing the intelligence agencies and banning political assassinations. However, the sensational revelations also spurred Congress to boost its institutional capacity by creating permanent select intelligence committees, and to pass legislation including the Foreign Intelligence Surveillance Act. Thirty years later, the FISA statute would set the stage for new battles over the executive’s electronic surveillance power in the global war on terror.

Foreign policy investigations also produced the greatest constitutional crisis of the 1980s. Congressional concerns, amplified by reports from investigators on the ground in Nicaragua, prompted Congress to pass a series of amendments barring the Reagan administration from covertly funneling aid to the Contra rebels. Revelations that the administration had clandestinely circumvented the ban triggered the nearly year-long Iran-Contra investigation, which rattled the very foundations of the Reagan presidency. While the legislation ultimately produced by the inquest was modest, its political damage to the president and the rest of his programmatic agenda was considerable.

How the Russia investigation will ultimately end remains uncertain. However, it has already shaped politics and policy outcomes in important ways. First, the investigation directly led to Robert Mueller’s appointment as Special Counsel. Mueller’s inquest likely poses the greatest legal threat to Trump and his associates. Second, by shining a bright light on Trump’s ties to Russia, the investigation increased pressure on Republican leaders – most of whom already disagreed with Trump’s lax stance on sanctions – to resist pressure to bottle up the bill and spare the president embarrassment and instead bring it to the floor. Finally, by weakening Trump and eroding his political capital, the investigation has created conditions in which some legislators from both sides of the aisle – skeptical of further misadventures in Afghanistan after sixteen years of indecisive fighting – might begin to push back against the administration’s planned escalation.

Investigations are far from a panacea, and the president remains the predominant actor in the international arena. However, by shining a light on alleged misconduct, investigations can affect strategic calculations on both ends of Pennsylvania Avenue and contribute to bursts of congressional reassertion in foreign affairs.

Kriner is a professor of political science at Boston University and the director of Graduate Studies. He is the author of "Investigating the President: Congressional Checks on Presidential Power" (Princeton 2016; winner of the 2017 Richard F. Fenno Jr. Prize and winner of the 2017 Richard E. Neustadt Award), with Eric Schickler. He also is the author of "The Particularistic President: Executive Branch Politics and Political Inequality" (Cambridge 2015; winner of the 2016 Richard E. Neustadt Award), with Andrew Reeves.

The views expressed by this author are their own and are not the views of The Hill.