Bill Wehrum spent only a year and a half as the Environmental Protection Agency’s top air official before announcing plans to resign Wednesday amid scrutiny over possible violations of federal ethics rules.

But during that time, Wehrum served as one of the chief architects of the Trump administration’s efforts to shrink the ambition and reach of the EPA, and to retreat from President Obama’s push to slash emissions of greenhouse gases and other pollutants. He oversaw efforts to ease regulation of the coal industry, slow requirements that cars and trucks become more fuel efficient and overhaul how the agency calculates costs and benefits to favor industry.

EPA Administrator Andrew Wheeler’s announcement Wednesday did not cite a specific reason for the departure of Wehrum, who as an attorney represented power companies seeking to scale back air pollution rules. But Wehrum has privately expressed concern about how an ongoing House Energy and Commerce Committee probe was affecting his former law firm, Hunton Andrews Kurth, according to individuals familiar with the matter who spoke on the condition of anonymity to discuss private conversations.

“While I have known of Bill’s desire to leave at the end of this month for quite sometime, the date has still come too soon,” Wheeler said Wednesday, praising Wehrum for “his service, his dedication to his job, the leadership he provided to his staff and the agency, and for his friendship.”

Environmental groups, Democrats on Capitol Hill and other critics were quick to celebrate Wehrum’s departure, calling him an integral part of the “swamp” that President Trump had vowed to drain in Washington.

“William Wehrum was emblematic of the administration’s struggles to remain ethical," Noah Bookbinder, executive director of Citizens for Responsibility and Ethics in Washington, said in a statement. "While it’s a good thing that Wehrum’s potential ethics problems will no longer affect the agency, the tone is set at the top, and if the EPA is to clean up the mess started by Scott Pruitt, the Trump administration needs to get serious about policing its ethical failures.”

Wehrum, who was confirmed in November 2017, is the latest Trump appointee to depart after coming under investigation for possible misconduct. Four Cabinet members — EPA Administrator Scott Pruitt, Health and Human Services Secretary Tom Price, Interior Secretary Ryan Zinke, and Veterans Affairs Secretary David Shulkin — have all left under an ethics cloud, along with other senior staffers such as Federal Emergency Management Agency Administrator William “Brock” Long.

Interior’s Office of Inspector General is currently investigating seven current or former top appointees for improperly engaging with their former employers or clients on department-related business, including Secretary David Bernhardt. Bernhardt has denied any wrongdoing, and the other officials have not commented publicly on the allegations.

The Energy and Commerce Committee launched its inquiry of Wehrum after The Washington Post reported in February that questions had been raised about his compliance with the Trump ethics pledge, which requires political appointees to recuse themselves from specific matters involving their former employers and clients for two years. If an appointee does meet with a former client, the pledge dictates that the gathering should be open to all interested parties — a requirement that has been interpreted to mean four other participants who were not clients.

Less than one month after joining the EPA, Wehrum met with two former clients at his old firm without consulting in advance with ethics officials, even though they had cautioned him about such interactions. That same month, Wehrum weighed in on a decision that appeared to benefit a former client, DTE Energy.

Wehrum, who heads the air and radiation office at the EPA, acknowledged both incidents in an interview with The Post but said he had determined that he did not violate federal ethics rules.

“I have, from day one, tried to be absolutely strict and assiduous as to what I do about complying with my ethical obligations,” Wehrum said, “because it doesn’t do me any good, and it doesn’t do the agency any good, to be doing things that people see as unethical.”

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Still, the fallout from the disclosure about Wehrum’s ties to his former firm and the utility industry by The Post and other outlets — including Politico, the New York Times and E&E News — has continued to reverberate. The Utility Air Regulatory Group, a collection of power companies that paid Hunton Andrews Kurth millions in membership dues, disbanded earlier this year.

Wehrum has said he represented the group as its own entity, rather than the individual utilities that made up its membership. But investigators on Capitol Hill have explored whether he and his former firm represented the power companies as well, according to one person familiar with the inquiry, raising the prospect that Werhum’s meetings could have violated ethics rules on multiple counts. The individual spoke on condition of anonymity because it is ongoing.

Both Wehrum’s supporters and his critics say that he has accomplished some of industry’s long-sought goals. In doing so, he has rolled back some of President Barack Obama’s most sweeping air policies. Last week the EPA finalized a rule targeting power plants that cuts carbon emissions by less than half of what experts say is needed to avoid catastrophic global warming. He has advanced other controversial proposals as well, including one that would slow efforts to improve gas mileage for cars and light trucks. Another would limit how the EPA calculates public health benefits in proposed regulations, which could make it tougher to limit pollution sources.

“No assistant administrator at EPA had more on their plate than Bill," Ross Eisenberg, vice president of energy and resources policy at the National Association of Manufacturers, said in a statement. "He executed the job with a steady hand and got big things done.”

But what some industry officials saw as Wehrum’s reasonable measures to reduce the regulatory burden on companies, critics describe as undermining the agency’s mission to protect public health and the environment.

“It is, at the very least, going to take years to undo the damage that has been done,” said John Coequyt, global climate policy director for the Sierra Club.

In a phone interview, Coequyt said that as Wehrum returns to the private sector, corporate clients could face blowback for enlisting Wehrum’s help. “We believe he’s toxic to their interests, and anyone who hires him will be publicly criticized for doing so."

Sen. Sheldon Whitehouse (D-R.I.), who joined other Democrats in February in asking EPA’s inspector general to investigate Wehrum, predicted that he would end up representing one of the companies that has sought regulatory relief from Trump’s EPA.

“I can’t wait to see where Bill Wehrum lands once he’s out the door,” Whitehouse said in a statement. “What do you bet it’s with one of the fossil fuel interests he has served so well as air chief, delivering one big handout after another?”