WASHINGTON (AP) — Interior Secretary Ryan Zinke, facing federal investigations into his travel, political activity and potential conflicts of interest, will be leaving the administration at year’s end, President Donald Trump said Saturday. In his resignation letter, obtained by The Associated Press, Zinke said “vicious and politically motivated attacks” against him had “created an unfortunate distraction” in fulfilling the agency’s mission.

Trump, in tweeting Zinke’s departure, said the former Montana congressman “accomplished much during his tenure” and that a replacement would be announced next week. The Cabinet post requires Senate confirmation.

Zinke is leaving weeks before Democrats take control of the House, a shift in power that promises to sharpen the probes into his conduct. His departure comes amid a staff shake-up as Trump heads into his third year in office facing increased legal exposure due to intensifying investigations into his campaign, business, foundation and administration.

Zinke’s resignation letter, obtained from a Zinke aide on Saturday, cites what he calls “meritless and false claims” and says that “to some, truth no longer matters.”

The letter, dated Saturday, said Zinke’s last day would be Jan. 2. It was not clear whether Zinke had already submitted the letter when Trump tweeted.

Zinke, 57, played a leading part in Trump’s efforts to roll back federal environmental regulations and promote domestic energy development. He drew attention from his first day on the job, when he mounted a roan gelding to ride across Washington’s National Mall to the Department of Interior.

Zinke had remained an ardent promoter of both missions, and his own macho image, despite growing talk that he had lost Trump’s favor. On Tuesday, Zinke appeared on stage at an Environmental Protection Agency ceremony for a rollback on water regulations. Mentioning his background as a Navy SEAL at least twice, he led the audience in a round of applause for the U.S. oil and gas industry.

Trump never established a deep personal connection with Zinke but appreciated how he stood tall against criticisms from environmental groups as he worked to roll back protections. But the White House concluded in recent weeks that Zinke was likely the Cabinet member most vulnerable to investigations led by newly empowered Democrats in Congress, according to an administration official not authorized to publicly discuss personnel matters who spoke on condition of anonymity.

His tenure was temporarily extended as Interior helped with the response to California wildfires and the West Wing was consumed with speculation over the future of chief of staff John Kelly. But White House officials pressured him to resign, the official said, which he did after his department’s Christmas party on Thursday night. On Saturday night, hours after his resignation became public, Zinke was spotted at the White House for another holiday party, the Congressional Ball.

As interior secretary, Zinke pushed to develop oil, natural gas and coal beneath public lands in line with the administration’s business-friendly aims. But he has been dogged by ethics probes, including one centered on a Whitefish land deal involving a foundation he created and the chairman of an energy services company, Halliburton, that does business with the Interior Department.

Reports surfaced this summer that a charitable foundation created by Zinke and run by his wife, Lola, was allowing a company co-owned by Halliburton chairman David Lesar to use the foundation’s land for a commercial development.

Lesar is a financial investor in 95 Karrow LLC, the company with plans to redevelop the former Idaho Timber mill site off West Second Street in Whitefish. The project involves a shared-use agreement between 95 Karrow and the Great Northern Veterans Peace Park Foundation for a parking lot to be built on the private park land known as the Great Northern Veterans Peace Park.

Zinke, though his foundation, expressed plans for a public sledding hill, but the park property remains undeveloped.

Investigators also are reviewing Zinke’s decision to block two tribes from opening a casino in Connecticut and his redrawing of boundaries to shrink a Utah national monument. Zinke has denied wrongdoing.

The Associated Press reported last month that the department’s internal watchdog had referred an investigation of Zinke to the Justice Department.

Zinke’s travels with his wife also had come under scrutiny.

Interior’s inspector general’s office said Zinke allowed his wife to ride in government vehicles with him despite a department policy that prohibits nongovernment officials from doing so. The report also said the department spent more than $25,000 to provide security for the couple when they took a vacation to Turkey and Greece.

Trump told reporters this fall he was evaluating Zinke’s future in the administration in light of the allegations and offered a lukewarm vote of confidence. Zinke in November denied he already was hunting for his next job.

“I enjoy working for the president,” he told a Montana radio station. “Now, If you do your job, he supports you.”

“I think I’m probably going to be the commander of space command,” Zinke said. “How’s that one?”

As head of Interior, Zinke made plans to realign the agency’s bureaucracy, trimming the equivalent of 4,600 jobs, about 7 percent of its workforce. He also proposed a massive overhaul that would have moved decision-making out of Washington, relocating headquarters staff to Western states at a cost of $17.5 million.

Zinke was a one-term Montana congressman when Trump selected him to join his incoming Cabinet in December 2016.

An early Trump supporter, Zinke is close to the president’s eldest son, Donald Trump Jr., and publicly expressed his interest in a Cabinet post when Trump visited Montana in May 2016.

Zinke’s critics were quick to comment following the announcement of his departure.

“Ryan Zinke will go down as the most anti-conservation Interior secretary in our nation’s history. By following President Trump’s marching orders to attack our public lands, Secretary Zinke oversaw an unprecedented and likely illegal attack on America’s national monuments,” Executive Director Jennifer Rokala of the Center for Western Priorities said. “Surrounding himself with former lobbyists, it quickly became clear that Ryan Zinke was a pawn for the oil and gas industry. We can expect more of the same from Acting Secretary David Bernhardt, but without the laughable Teddy Roosevelt comparisons.”

“Sec. Zinke leaves behind a deeply troubling legacy,” Montana Wilderness Association’s Executive Director Ben Gabriel said. “He shrank and endangered national monuments, invited the oil and gas industry to seize and exploit some of our most cherished public lands in Montana, and stripped the public from having a say over the future of those lands. He also hired numerous people at the Department of the Interior who have spent their careers trying to transfer or sell off public lands. Montanans deserve and expect public officials who will protect our public lands in support of our outdoor way of life.”

“Ryan Zinke’s tenure at the Department of Interior was a disaster for public lands of historic proportions,” said Western Values Project Executive Director Chris Saeger. “The public and Congress should continue their commitment to vigilant oversight over the ongoing ethical abuses at Interior in order to repair its reputation.”

While Zinke shrunk monuments in Utah, he suggested creating one in the Badger-Two Medicine region just south of Glacier National Park. In addition, he also went ahead with an appeal of a court ruling that would allow some oil and gas exploration in that area.

Some have speculated he did that in order to run for Montana governor in 2020.

The Whitefish Pilot and Hungry Horse News contributed to this report.