The U.S. Capitol dome is seen at sunset on Capitol Hill, Friday, Nov. 18, 2016 in Washington. (AP Photo/Alex Brandon)

How is Congress getting its work done? Health care, tax reform, and investigations into the Trump campaign’s potential connections to Russia all require staff time and effort.

And yet the number of staffers supporting congressional committees has dropped significantly — so much so that some critics question whether Congress has enough support to write thoughtful legislation and effectively oversee an expanding and ever-stronger executive branch.

But our new research finds that just counting Hill staff overlooks an important source of expertise for congressional committees: Executive agency “detailees.” Agencies loan these civil servants, who embed temporarily within congressional committees and help them do their work.

Borrowing staff from executive agencies can be a win-win solution for both branches. Congress rebuilds its capacity at no cost. Agencies gain valuable legislative intelligence from moles on Capitol Hill. Some argue detailees are another way the executive exerts its influence over Congress while giving members an excuse not to hire additional permanent staff.

Congressional committee staff have been sharply reduced

As you can see in the figure below, both House and Senate committee staff have declined sharply between 1977 and 2014.

Why? Three factors drive the decline. First, in today’s polarized and partisan climate, members of Congress have been increasing staff in offices back home and in their own personal offices on the Hill to better handle constituent requests. Second, as power has flowed from committees to party leaders in both the House and Senate, the committees’ role has significantly waned. With federal discretionary spending limited, leadership offices gain funding while committees lose.

What are detailees and how are they selected?

Detailees are often mid-career civil servants who have particular expertise in agency policy or knowledge of internal decision-making. Details are temporary assignments, typically lasting a year. Detailed employees remain on their home agencies’ payroll while serving in Congress. That gives Congress a low-cost method of supplementing committee resources.

To identify these detailees, we combed through congressional directories and relied on official records from the Senate Committee on Rules and Administration. The figure above shows how much committees’ detailees have increased between 1997 and 2015. As the number of committee staff decreased by 35 percent in the House and 15 percent in the Senate over the past 20 years, the number of detailees has increased by over 300 percent.

Committee staff directors from both the majority and minority party often select detailees from agency staff with whom they interact on a regular basis and the directors believe will, as one staff director noted, “preferably be politically sympathetic” to the committee’s partisan affiliation.

The committee chair under which a detailee will work and the House Committee on House Administration or the Senate Committee on Rules and Administration must sign off on all details. Requests for detailees from the minority party are typically approved – probably because the majority party fears retribution when, sometime in the future, it becomes the minority.

So why would an agency agree to sacrifice a staff member for Congress’s use? They may feel political pressure. As one committee staff director told us,

I’ve been turned down by every agency I’ve requested [a detailee] from. Then it typically requires me to have a conversation with the secretary of the agency. Currently we have four detailees [from other agencies] on our investigations unit. I tell the secretaries, we can have them doing other things or investigating your agency. So typically, the Secretary and I will come to some kind of mutual understanding. I’ve never not gotten someone I’ve wanted.

Both branches gain from detailees

Our sources, including committee staff directors and detailees, told us that they gained from these assignments.

Congressional committees benefit in more ways than are immediately obvious, we found. First, these executive agency staffers bring deep knowledge and expertise in specific policy areas that traditional committee staff may not possess, thereby helping committees craft more effective legislation.

Second, detailees help committees oversee federal agencies, including their home agencies. They put staff in touch with executive branch staffers who can respond quickly to requests for information or input on legislation.

Interestingly, we find that when committees have more detailees, they hold fewer oversight hearings. That may be because detailees can give committees the information they need about what agencies are doing.

Third, detailees help the committee manage the groups interested in their subject. Many agency staffers routinely work with a different set of stakeholders than do committee staff. We found that committees that have more contact with interest groups rely more heavily on detailees than do others.

And of course, Congress increases its institutional capacity — without having to vote to give itself more resources, something that’s unpopular among constituents.

So what do the agencies get out of this (besides, of course, fewer oversight hearings)? First, they get a direct conduit with insight into congressional decision-making. Second, detailees represent their agencies’ interests and perspectives on the Hill.

Could there be a downside? Detailees shift the balance of policymaking power even further towards the executive while providing a disincentive for Congress to hire more permanent staff. However, detailees are now a critical and institutionalized part of how Congress functions.

In other words, as Congress tackles its challenging agenda, executive agency staffers are likely to be critical in crafting legislation, unearthing information — and in some cases investigating — the very agencies that pay their salaries.

Russell W. Mills is an associate professor of political science at Bowling Green State University in Ohio and a former policy analyst at the Federal Aviation Administration.

Jennifer L. Selin is an assistant professor of political science at the Kinder Institute at the University of Missouri.

This research was supported by a grant from the Dirksen Congressional Research Center.