Former Oklahoma Attorney General Scott Pruitt’s 16-month tenure as administrator of the Environmental Protection Agency came to a screeching halt Thursday.

President Trump tweeted Thursday he accepted Pruitt’s resignation. Trump said the agency’s deputy administrator and former coal industry lobbyist, Andrew Wheeler, will become acting head of EPA, Kallanish Energy reports.

The departure follows months of scrutiny that gathered momentum following reports Pruitt had rented a Capitol Hill condominium linked to an energy lobbyist on favorable terms.

The news exacerbated concerns about the high cost of Pruitt’s travel and security detail and triggered a flood of allegations Pruitt fostered a culture of workplace retaliation, wasteful spending and self-dealing at EPA.

“It is extremely difficult for me to cease serving you in this role first because I count it as a blessing to be serving you in any capacity, but also because of the transformative work that is occurring,” Pruitt said in his resignation letter.

“However, the unrelenting attacks on me personally, my family, are unprecedented and have taken a sizable toll on all of us.”

While Pruitt was a key figure in Trump’s campaign to roll back environmental regulations, he increasingly became seen as a liability in an administration that has seen two Cabinet members fired over ethical lapses and several more accused of wasting taxpayer dollars.

The EPA administrator also reportedly alienated colleagues by positioning himself to take over as U.S. attorney general if the frequently embattled head of the Justice Department, Jeff Sessions, stepped down or was fired.

Pruitt became a lightning rod from the moment Trump nominated him. The Oklahoman rose to prominence as the state’s attorney general, where he developed close ties to the energy industry and sued the EPA more than a dozen times.

As EPA administrator, Pruitt said the agency’s primary responsibility is to offer certainty to the energy companies, automakers and other business interests it regulates. He sidelined agency scientists, sought to ease environmental rules and encouraged staff to think of the companies it regulates as its customers.

He stood with the President on issues that divided the administration, like pulling the U.S. out of the Paris climate agreement.

Pruitt came under scrutiny last year for his frequent travel, sometimes in first class, to his home state. The EPA’s inspector general opened an investigation into the matter in August.

Pruitt’s travel habits came back into focus earlier this year as reports showed the EPA chief and staffers had spent at least $90,000 on traveling just a few days in January, including for first-class airfare. The EPA defended Pruitt’s pricey itineraries, saying his security detail had ordered him to travel first class due to several threats against the administrator and unspecified incidents during previous trips.