WASHINGTON — Interior Secretary Ryan Zinke, facing federal investigations into his travel, political activity and potential conflicts of interest, will leave the administration at year’s end, Trump said Saturday.

In his resignation letter, 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 this 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 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.

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 replacement of chief of staff John Kelly.

But White House officials pressured him to resign, the official said, which he did after his final public appearance at his department’s Christmas party on Thursday night.

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 Montana land deal involving a foundation he created and the chairman of an energy services company, Halliburton, that does business with the Interior Department.

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, Lola Zinke, 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 bars nongovernment officials from doing so.

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.”

Zinke outlasted EPA chief Scott Pruitt, another enthusiastic advocate of Trump’s business-friendly way of governing who resigned in July amid ethics scandals.

Democratic leaders in Congress were scathing in response to the news that Zinke was leaving.

“Ryan Zinke was one of the most toxic members of the cabinet in the way he treated our environment, our precious public lands, and the way he treated the govt like it was his personal honey pot,” Senate Minority Leader Chuck Schumer tweeted Saturday. “The swamp cabinet will be a little less foul without him.”