Now that Draining The Swamp is back on the agenda—and it definitely is, Donald Trump says—folks who labor in the myriad federal buildings dotting Washington are probably thinking about their options. How will Trump approach the federal government’s 2.5 million federal employees, or the 7,000-odd senior managers who assist political appointees? Will they even want to stay?

Signs point to an exodus. A study published earlier this month suggests that senior civil servants leave in droves during the first year of a new administration. They’re especially likely to quit when the incoming president’s politics are counter to the agency’s own ideological leanings.

And when these leaders leave, they take their experience and connections with them, leaving federal departments worse off.

“The government is a bundle of expertise,” said John de Figueiredo, a professor of law, strategy, and economics at Duke University, who co-authored the study. “When you lose these people who are very senior, we think that could potentially have a detrimental effect on governmental performance.”

The idea that agencies even have ideological leanings might raise a few eyebrows. They’re supposed to be apolitical, after all. And the paper’s logic presumes that most employees would fall in line with their agencies’ reputations. But data collected through years of surveys indicate government departments do have political preferences, and the study’s authors say there’s strong evidence linking those preferences to the departure of senior managers under unfriendly administrations.

To prove their point, researchers cracked open a massive employee database from the Office of Personnel Management, spanning 23 years and millions of workers. Electing a new president had almost no effect on the rank-and-file members of government, they found. Instead, most of the departures came from the Senior Executive Service, the elite cadre of managers who are often the primary layer between the appointees the president picks and the rest of the federal workforce.

Formed in 1978, the SES was designed to ensure continuity between administrations, an squad of generalists who could jump into a department and make it better. As my colleague Nora Kelly reported earlier this year, it hasn’t quite lived up to that promise; its leaders tend to get siloed within single agencies. But getting into the SES is quite competitive; as de Figueiredo puts it, the folks are undeniably “high performers.”

How could this play out under a Trump administration? Well, the president-elect has already nominated a climate-change denier to head the Environmental Protection Agency, and he wants to hand control of the Department of Energy to a man who’d prefer to abolish it. Plus, he’s a Republican. The study’s model would suggest a spike in departures from liberal-leaning agencies, including the EPA, the Department of Education, and the Department of Housing and Urban Development.

On the other end, the model expects to see more stable employment at more conservative branches, including the military. Indeed, Trump was endorsed by unions representing both agents in both the Border Patrol and Immigration, Customs and Enforcement, whose ranks will almost certainly swell if the president-elect gets his way.

Can the loss of experienced managers be prevented? “Some presidents who enter office have tended to be skeptical and suspicious of career employees,” said the study’s co-author, Alexander Bolton, a political science professor at Emory University. “But management strategies and the inclusion of career employees might help mitigate this mistrust.” Civil-service employees fear being ignored, just as much as presidents fear being undermined.

Given Trump’s adversarial stance toward government, Washington will likely see turnover. What this means for the long term isn’t clear. The machinery of government has always chugged along, even amid the most dramatic transfers of power. But as the president installs his own people at the top, and skeptical bureaucrats who report to them depart, the agencies begin to look more like him.

For conservatives, that might be a boon—a way to remake government along more congenial lines. But it could also be an impediment to a president with an ambitious agenda, thinning out the ranks of professionals who possess the knowledge necessary to navigate a complicated bureaucracy and implement policies swiftly and effectively. It’s hard to push through policies over the active resistance of the people charged with implementing them, but it can be just as hard to implement them without experienced managers capable of putting plans into action.