Interior Secretary Ryan Zinke, whose departure from the Trump administration was announced Saturday via presidential tweet, said in his resignation letter that “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.

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.

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

“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 of the New York tweeted Saturday. “The swamp cabinet will be a little less foul without him.”

House Minority Leader Rep. Nancy Pelosi, who is set to become speaker in January, said Zinke had “been a shameless handmaiden for the special interests” and his “staggering ethical abuses have delivered a serious and lasting blow to America’s public lands, environment, clean air and clean water.”

Zinke got a warmer send-off from Republican Sen. Lisa Murkowski of Alaska, head of the Energy and Natural Resources Committee, who said in a statement that he had been a “strong partner for Western states.”

David Bernhardt, the deputy secretary and who grew up in Colorado, is in line to lead the Interior Department on an interim basis. He has spent years in Washington as a lobbyist for the oil and gas industry and has deep ties to Republican politicians and conservative interest groups.

Two outgoing Republican congressmen are said to be interested in the job.

Rep. Raul Labrador of Idaho planned to go to the White House to discuss the job with officials, said a GOP congressional aide who spoke on condition of anonymity to describe Labrador’s private plans. Labrador, 51, a member of the conservative House Freedom Caucus, who is retiring from Congress after eight years. He lost a bid for his state’s GOP gubernatorial nomination last spring.

Rep. Jeff Denham, R-Calif., is also interested in Zinke’s job, according to another Republican congressional aide who described the situation only on condition of anonymity.

The aide said the White House has made inquiries about Denham to Rep. Kevin McCarthy, R-Calif., who will be House minority leader next year. Denham, 51, has been involved in water issues in California. He lost his bid for re-election last month.

Zinke was a one-term 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.