WASHINGTON — On the campaign trail, Donald Trump vowed to dismantle the Environmental Protection Agency "in almost every form. We're going to have little tidbits left, but we're going to take a tremendous amount out."

As president, he is making headway on that promise.

During the first 18 months of the Trump administration, records show, nearly 1,600 workers left the EPA, while fewer than 400 were hired. The exodus has shrunk the agency's workforce by 8 percent, to levels not seen since the Reagan administration. The trend has continued even after a major round of buyouts last year and despite the fact that the EPA's budget has remained stable.

Those who have resigned or retired include some of the agency's most experienced veterans, as well as young environmental experts who traditionally would have replaced them — stirring fears about brain drain at the EPA. The sheer number of departures also has prompted concerns over what sort of work is falling by the wayside, from enforcement investigations to environmental research.

According to data released under the Freedom of Information Act and analyzed by The Washington Post, at least 260 scientists, 185 "environmental protection specialists" and 106 engineers are gone.

Several veteran EPA employees, who have worked for both Republican and Democratic administrations, said the agency's profound policy shifts under Trump hastened their departure.

"I felt it was time to leave given the irresponsible, ongoing diminishment of agency resources, which has recklessly endangered our ability to execute our responsibilities as public servants," said Ann Williamson, a scientist and longtime supervisor in the EPA's Region 10 Seattle office.

She left in March after 33 years at the agency, exasperated by having to plan how her office would implement President Trump's proposed cuts and weary of what she viewed as the administration's refusal to make policy decisions based on evidence. "I did not want to any longer be any part of this administration's nonsense," she said.

In a statement Friday, Acting Administrator Andrew Wheeler said he was focused on right-sizing the EPA, which Republicans have argued overreached under President Barack Obama, burdening industry with regulations such as those focused on climate change.

"With nearly half of our employees eligible to retire in the next five years, my priority is recruiting and maintaining the right staff, the right people for our mission, rather than total full-time employees," he said.

Congress has so far maintained the EPA's budget at just more than $8 billion, and while current proposals could shrink that amount, any cuts are likely to be modest.

"The Trump administration comes in and goes way, way beyond what the budget requires," said Rep. David Price, D-N.C., a senior member of the House Appropriations Committee and whose district is home to a major EPA research center. Price said multiple constituents have told him that working at the EPA has become "intolerable" after seeing their findings sidelined.

"It is profoundly demoralizing, and I think, profoundly damaging in terms of the agency's mission," he said.

The EPA is not alone in shedding personnel under Trump, despite the fact that Congress passed a $1.3 trillion budget bill in March that boosted both military and domestic spending.

The State Department's total number of permanent employees, for instance, fell 6.4 percent between Trump's inauguration and March 2018, according to federal records, while the Education Department declined 9.4 percent during that time.

Part of the drop stems from a government-wide hiring freeze Trump imposed after his inauguration, which lasted nearly three months. The president has continued to press for a leaner federal payroll, asking Congress recently to withhold pay raises for federal workers in 2019.

In a few instances, Trump's deputies are trying to fill the widespread vacancies in their department's ranks. Secretary of State Mike Pompeo recently began trying to staff the many senior positions that remained empty under his predecessor, Rex Tillerson. Meanwhile, Veterans Affairs is eager to hire doctors, nurses and other medical professionals to fill thousands of vacancies.

But at the EPA, it is largely a case of career staff members headed for the exits. Hundreds of employees accepted buyouts last summer, and records show that nearly a quarter of the agency's remaining 13,758 employees are now eligible to retire. At its peak in the late 1990s, the EPA employed more than 18,000 people.

-- The Washington Post