Research shows that military veterans in Congress, like Sen. John McCain (R-Ariz.), who was a prisoner of war in Vietnam, are more likely to take an active role in overseeing a president’s use of force and military deployments. (J. Scott Applewhite/AP)

With four U.S. soldiers killed in Niger, debate has begun again about how much power Congress should have — or use — to oversee foreign military operations. That has included Senate Foreign Relations Committee hearings on a new Authorization for the Use of Military Force (AUMF).

But there’s another important question, as well: How and when does Congress rein in the president’s military decisions?

Scholars traditionally argue that Congress has done little to oversee military policy. But some new research suggests that Congress may indeed be able to constrain the White House in its decisions about when and how to use military force — especially, my research shows, if enough members of Congress are military veterans.

Here’s how I did my research

For my recently published article in Political Research Quarterly, I collected data on U.S. House of Representatives roll call votes about military operations from 2003 to 2012 in the wars in Iraq and Afghanistan.

I found that members of Congress with military experience showed two key differences from nonveterans on such votes:

  • Veterans were more willing to limit the number of troops deployed in Iraq and Afghanistan, or to want to bring troops home from these wars.
  • Veterans were more likely to vote for increased congressional access to information about these military conflicts.

In other words, members of Congress with military service were more willing to oversee and restrain the White House’s military deployments.

This wasn’t because of partisanship or political affiliation. True, under both Presidents Barack Obama and George W. Bush, veterans from the party opposite the president’s were more likely to want to rein in the administration. But, in general, members of Congress who were military veterans were simply more likely to cast their votes in favor of getting critical information about how military force was being used.

This shows that having veterans in the legislature can encourage Congress to be more active in overseeing foreign military operations. Congress gets more and higher-quality information about war operations because these veterans are more willing to push for access to such information. This, in turn, makes it easier for Congress to weigh in on the use of military force.

The percentage of members of Congress who served in the military is going down

A number of scholars and pundits have been sounding the alarm over the ongoing decline of military veterans in Congress. Some warn that this will lead to a Congress that’s more deferential and less effective in checking the president on military and defense policy.

How much has the percentage of military veterans in Congress declined in recent decades? According to the Pew Research Center, in 1967, veterans made up 75 percent of the House; in 1975, they made up 81 percent of the Senate. These peak numbers reflect the substantial proportion of those generations that served in World War II.

But since the mid-1970s, those percentages have been declining, just as the proportion of Americans who have served in the military has declined. The Congressional Research Service reports that only 18.8 percent of members of Congress in the current session have performed some form of military service. Yet, compared with the percentage of the general public that has served in the armed forces, veterans in Congress are overrepresented.

Will the proportion of veterans decline even further after the 2018 midterms?

After the 2016 election, more veterans entered Congress than had done so in previous election cycles; they had served in recent wars, such as Iraq and Afghanistan. But some estimate that, as members who served in Korea and Vietnam retire, the number of veterans in Congress could drop dramatically in the next session. The number of new veterans entering Congress may just not be enough to replace older veterans who retire or fail to win reelection.

That might be countered by the fact that political parties actively recruit veterans to run for office, believing that a history of military service attracts voters. Using experiments, researchers show that the public views veterans as more credible and as a source of authority on foreign and defense policy.

But, in practice, it’s not clear whether this holds true during actual elections, at least for Democrats. In 2006, candidates who were veterans performed well in Democratic primaries, but if nominated, they had mixed success in the general election.

Does it matter if Congress has fewer members who are military veterans?

In brief, yes. Fewer veterans in Congress could probably result in a decreased willingness by the legislature to try to influence the White House on defense and national security initiatives. With less willingness to question the White House on uses of military force, it will simply be harder for Congress to do its job as a foreign policy watchdog and adviser, especially as a Congress with fewer veterans may also lead to a less transparent White House.

Consider the fact that many Americans were shocked not only by the recent deaths of U.S. service members in Niger, but also by the fact that the United States was militarily involved in Africa. Several senators publicly objected that they had not been apprised of the operation, although the Pentagon maintains that Congress was appropriately informed.

What does all this mean for the ongoing debate over the AUMF?

In short, Congress may be less willing to repeal the existing AUMF and more willing to pass a new one if the White House’s pressure isn’t offset by veterans who are senators and representatives. Without those veterans’ public credibility and personal confidence in questioning the administration about military operations, Congress may well become a far tamer watchdog, lacking the information it needs to prevent oversteps by the executive.

Danielle Lupton is an assistant professor of political science at Colgate University, where she studies the influence of political elites on foreign policy and national security. She is working on a book titled “Leaders, Perceptions, and Reputations for Resolve.”