Interior Department Secretary Ryan Zinke submitted his resignation to the White House on Saturday, facing intense pressure to step down because of multiple probes tied to his real estate dealings in his home state of Montana and his conduct in office.

President Trump announced Zinke’s exit via Twitter on Saturday morning and praised the departing Interior chief. “Secretary of the Interior @RyanZinke will be leaving the Administration at the end of the year after having served for a period of almost two years,” the president tweeted. “Ryan has accomplished much during his tenure and I want to thank him for his service to our Nation.”

Behind the scenes, however, the White House had been pushing Zinke for weeks to resign, administration officials said. Last month, the officials said, Zinke was told he had until the end of the year to leave or be fired.

Zinke — 57 and the first Montanan to have served in a presidential Cabinet — is the fourth member of Trump’s Cabinet to resign under an ethics cloud in less than two years. Health and Human Services Secretary Tom Price, Veterans Affairs Secretary David Shulkin and Environmental Protection Agency Administrator Scott Pruitt also relinquished their posts amid scrutiny on subjects including how they spent taxpayer money on their travel.

For Zinke, the key moment in his loss of support at the White House came in October, when Interior’s inspector general referred one of its inquiries to the Justice Department, according to two senior administration officials who spoke on the condition of anonymity to discuss a sensitive matter.

That probe, which continues, is examining whether a land deal Zinke struck with the chairman of oil services giant Halliburton in his hometown of Whitefish, Mont., constituted a conflict of interest.

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Photo Gallery: Thirty-three notable officials, from Kevin McAleenan to Sally Yates, have quit or been fired.

Zinke blamed his departure in a private resignation letter, obtained by The Washington Post, on “vicious and politically motivated attacks.”

In a tweet Saturday afternoon, he said, “I love working for the President and am incredibly proud of all the good work we’ve accomplished together. However, after 30 years of public service, I cannot justify spending thousands of dollars defending myself and my family against false allegations.”

As the leading advocate for Trump’s push to expand domestic energy production, the former Navy SEAL and congressman from Montana became a lightning rod for controversy. He was hailed by energy industry officials for relaxing Obama-era environmental rules and opening up large areas of federal land and waters for oil and gas prospecting. But environmental groups assailed his policies and conducted opposition research into his management practices and financial dealings.

Though Zinke won Senate confirmation by a vote of 68-to-31, views on him divided sharply along partisan lines as he promoted U.S. “energy dominance,” a phrase he often uttered when laying out department policy.

Senate Energy and Natural Resources Committee Chairman Lisa Murkowski (R-Alaska), who successfully lobbied the Trump administration to restart energy exploration in the Arctic National Wildlife Refuge, said in a statement that she “was disappointed to learn that Secretary Zinke is stepping down.”

“He has been a strong partner for Western states and for Alaska, in particular,” Murkowski said. “After years of frustration with the Department, he came in and took a very different approach — he listened to us, built a great team, and worked with us to advance our priorities.”

Several advocacy groups welcomed his departure, even as they pivoted to attack Deputy Interior Secretary David Bernhardt, who will take over in the interim. Bernhardt, a skilled policy expert who has steered most of the department’s key policy decisions since joining in August 2017, is one of several Western Republicans who might be considered for the job.

“Ryan Zinke will go down as the most anti-conservation Interior secretary in our nation’s history,” Jennifer Rokala, executive director of the Center for Western Priorities, said in a statement. “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.” Zinke had styled himself as a Teddy Roosevelt Republican, showcasing his love of hunting, fishing and riding in the Montana wilderness.

Kathleen Sgamma, president of the Western Energy Alliance, said in an email that liberal activists might end up regretting their push to oust Zinke.

“The environmental groups have claimed another scalp, but as with Pruitt, they’re going to be disappointed,” said Sgamma, whose group represents several oil and gas firms. “The deputy secretary will move forward with the energy dominance agenda, and there’s no sign from the president that he’ll appoint another secretary who’s not on board with the successful job creation that results from that agenda.”

Administration officials concluded weeks ago that Zinke was the Cabinet member most vulnerable to congressional investigations once Democrats took control of the House in January. But multiple crises, including wildfires out West and uncertainty over whether John F. Kelly would stay on as White House chief of staff, had afforded Zinke a temporary reprieve.

During his tenure, Zinke came under at least 15 investigations, including: inquiries into his connection to a real estate deal involving a company that Interior regulates; whether he bent government rules to allow his wife to ride in government vehicles; and allowing a security detail to travel with him on a vacation to Turkey at considerable taxpayer cost.

Zinke was cleared in several of those investigations, and he attacked his critics rather than adopt a more chastened tone. Late last month, he accused Rep. Raúl M. Grijalva (D-Ariz.) — who had called on Zinke to step down and is poised to take over the committee that oversees Interior in January — of being a drunk.

“It’s hard for him to think straight from the bottom of the bottle,” Zinke wrote from his official Twitter account on Nov. 30. Grijalva, who in the past had acknowledged having a problem with alcohol but said it had been addressed, said the committee would not be distracted from examining Zinke’s actions.

It is unclear whether the federal inquiries will continue when Zinke leaves office.

On Saturday, Grijalva said in a statement, “This is no kind of victory, but I’m hopeful that it is a genuine turning of the page.”

“Secretary Zinke’s successor has a chance to move on from an unfortunate Trump administration record of environmental mismanagement and decline,” he added. “A well-managed Interior Department — one that puts the public good ahead of fossil fuel and mining industry demands — can be a boon to the entire country.”

Although Zinke remained defiant in public and private this month — less than two weeks ago, he boasted that he would continue to attack his critics — Trump had little personal affection for him. The president was annoyed by a few of Zinke’s actions, including his announcing in a January appearance with Florida Gov. Rick Scott (R) that the state would be exempted from offshore drilling, a commitment that was not approved in advance by the White House, and a decision to allow imports of elephant trophies. Zinke reversed the decision on elephant trophies after Trump publicly intervened.

The secretary’s final public appearance was Thursday night at his office Christmas party, which he told White House staffers he wanted to have before his dismissal. He invited lobbyists and conservative activists to his executive suite, where he posed for photos in front of a large stuffed polar bear wearing a Santa cap, according to an attendee.

Mounted animals on the walls were fitted with ornaments.

“He still has big-time political ambitions,” said one Republican with close ties to Zinke, who spoke on the condition of anonymity to comment frankly.

The jockeying to replace Zinke as secretary has already begun, according to Republicans who have been engaged in discussions with the administration.

In addition to Bernhardt, the GOP candidates include outgoing Sen. Dean Heller (Nev.), Reps. Raúl R. Labrador (Idaho), Jeff Denham (Calif.), Cathy McMorris Rogers (Wash.), and Rob Bishop (Utah), who next month will relinquish his chairmanship of the House Natural Resources Committee.

Zinke’s resignation, which comes after Trump replaced his attorney general and White House chief of staff, could be followed soon by other Cabinet departures. The positions of Homeland Security Secretary Kirstjen Nielsen and Commerce Secretary Wilbur Ross remain precarious, according to White House officials.

For the moment, Democrats such as Senate Minority Leader Charles E. Schumer (N.Y.) seem eager to crow about the latest departure.

“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 government like it was his personal honey pot,” Schumer said in a tweet. “The swamp cabinet will be a little less foul without him.”

Lisa Rein and Mike DeBonis contributed to this report.