A day after the Senate made Ryan Zinke the first Montanan to serve in a presidential Cabinet, the new Interior secretary put on a black cowboy hat, mounted a horse named Tonto and paraded across the Mall with a U.S. Park Police detail to the front doors of Interior’s downtown Washington headquarters.

At that moment last year, Zinke sat tall in the saddle. He was a one-term congressman who had blazed a political trail in his home state. His star was so bright that Senate Majority Leader Mitch McConnell (R-Ky.) lobbied against his Cabinet appointment, thinking Zinke was almost a sure bet to defeat Sen. Jon Tester (D-Mont.), who was reelected this year. To some liberal conservationists, Zinke appeared to be a conservative who could bridge the partisan divide. The Senate confirmed him with 68 votes.

But Zinke was anything but bipartisan. His zeal in carrying out President Trump’s vision of “American energy dominance” by boosting coal and gas production on public lands angered Democrats who supported him, and his tendency to overstep the limits of his power at Interior worried Republicans and the president.

When he abruptly resigned 10 days before Christmas, Zinke was facing five active federal investigations. During his brief 21-month tenure, he racked up a total of 15 probes into his management and behavior. Now the political future of the ex-Navy SEAL who so quickly found national prominence isn’t so bright.

Given Montana’s conservative bent — Trump won the state in 2016 by nearly 20 points — a political comeback could still be possible. Zinke took pains to protect certain areas in the state even as he opened up land outside Montana to drilling and mining. A week ago, for example, he announced that the Bureau of Land Management had spent just over $1 million to acquire 960 acres of land within Montana’s Little Sheep Creek. And he’s not going away quietly: Zinke has a scheduled interview with Fox News at 6 p.m. Thursday.

“I still think he’s got a lot people who vote for him, but I think it will be much tougher for sportsmen, in particular, to support him,” said Land Tawney, president of Backcountry Hunters & Anglers and a fifth-generation Montanan.

Tawney said that even though Zinke decided against altering a national monument in Montana, the fact that he helped shrink two in Utah has made all federally protected areas vulnerable. “He set the precedent for doing that,” he said.

“He rode into D.C. on a horse in an English saddle,” Tawney said, adding that a true Westerner, as the secretary claims to be, would’ve chosen a Western saddle. “That just kind of shows there’s a disconnect in how he likes to see himself. He doesn’t practice what he preaches.”

Among Zinke’s final acts before his resignation was a holiday party at Interior that he told the White House he wanted to host before his dismissal. On a wall in his office were hunting trophies of bison and elk heads that he’d ordered workers to mount. In a corner was the stuffed carcass of a grizzly, with a Santa’s cap perched on its massive head. The secretary’s signature collection of large military assault knives was nearby.

Shortly after he arrived at Interior, Zinke installed an arcade game that simulated hunting and killing in a common area to reaffirm his avid support for the sport. Finally, Zinke ordered staff to fly a secretarial flag over the building, and to raise and lower it when he came and went. No one could recall a similar ritual ever happening in the federal government.

Those were just the little changes.

Zinke wasted no time in fulfilling Trump’s promise to Sen. Orrin G. Hatch (R-Utah) and others in the state’s congressional delegation to dramatically reduce two popular national monuments designated by Democratic presidents. He cut the acreage of Bears Ears by 85 percent and Grand Staircase-Escalante by 46 percent, a feat no other Interior secretary had attempted.

At the same time, Zinke executed Trump’s “American energy dominance” agenda to exploit federal land and waters for coal, oil and gas production. Under Trump, nearly 95 million acres of public land and water have been offered for oil development, an area the size of Montana, according to the Wilderness Society, a conservation group. The 153 million acres of land and water that Interior stripped of federal protection is larger than California and Washington combined, the group said.

To some, this approach struck the right balance. “Thank you, Secretary Zinke, for restoring commonsense management of our public lands, fighting to end the war on coal and for making the U.S. energy dominant,” Sen. Steve Daines (R-Mont.) tweeted after Trump announced that Zinke would leave Interior at the end of the year. “Montana is proud of you!”

But it turned others against him. Collin O’Mara, the National Wildlife Federation president who attended a meet-and-greet with Zinke on his first day in office, blasted him in an opinion piece published by The Washington Post.

Zinke’s lasting legacy won’t be the investigations he faces; it “will be the millions of acres of public lands degraded, the climate pollution increased, the outdoor recreational opportunities forsaken, the national monuments decimated and the wildlife species imperiled by an all-consuming energy dominance agenda,” O’Mara wrote Sunday.

Critics contrasted Zinke’s actions with those of Theodore Roosevelt, the former Republican president the secretary often cited as his hero.

Roosevelt “set aside roughly 300 million acres of the federal estate for the use of all Americans,” said Tracy Stone-Manning, associate vice president for public lands at the National Wildlife Federation. Roosevelt’s conservation includes 79 wildlife refuges, game reserves, national parks and national monuments.

In service to Trump, Zinke pursued the most ambitious expansion of offshore leasing in history, proposing a plan to open nearly the entire U.S. outer continental shelf to the oil and gas industry, including the Pacific and Arctic oceans, along with the Atlantic, where drilling had not happened in about five decades. Every governor except Maine’s eventually opposed it.

What happened in the week after Zinke announced the proposal in early January probably contributed to his downfall. Without informing the president, Zinke flew to Florida to meet with Gov. Rick Scott (R), a Trump backer and a onetime supporter of drilling who was mulling a Senate run.

Zinke assured Scott that Florida would be exempt from the plan, a promise that stood to help the governor against Sen. Bill Nelson (D), a fierce opponent of drilling and Trump. The maneuver backfired, angering Trump, who favored drilling off Florida, and nearly every governor who wanted the same deal.

Within weeks, Interior’s inspector general opened an investigation into the matter. But the investigation that hurt Zinke most was yet to come.

During the summer, Politico revealed that Zinke might have been in talks with the chairman of Halliburton, an oil services company that Interior regulates, regarding a commercial development in his hometown of Whitefish, Mont.

Soon after, the inspector general opened a probe to determine whether Zinke was using his office to enrich himself. The White House became concerned about the case after it was forwarded to the Justice Department for a possible criminal investigation.

The Office of Special Counsel said it can’t confirm or deny whether cases are open or closed, but investigations “typically continue even after the subject . . . leaves federal service,” said spokesman Zachary Kurz. Justice has a similar policy.

Zinke has also been investigated over allegations that he broke federal rules by reassigning senior employees without proper notice, violated ethics by misusing aircraft for travel and disregarded departmental regulations by allowing his wife to travel in government vehicles.

At least 10 of the investigations against Zinke were closed with a finding of no wrongdoing. Last month, for example, the inspector general found no evidence that Interior redrew the boundaries of Utah’s Grand Staircase-Escalante National Monument for a state lawmaker’s financial benefit.

Even as whispers of his ouster swirled around Washington in November, Zinke disputed notions that he had done anything wrong. “The allegations against me are outrageous; they’re false,” he told Breitbart News on SiriusXM Patriot, a conservative talk radio channel. “Everyone knows they’re false.”

Zinke declared that a “resistance movement” of activists angry about his policies was spreading rumors and threatening his wife and children. He demeaned the ethics probes into his activities as “fake news” and vowed to stay on the his job, saying the president backed him “100 percent.”

He was mistaken. On Saturday, Trump tweeted that Zinke “will be leaving the Administration at the end of the year after having served for a period of almost two years."

Zinke followed Trump’s tweet with his own: “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.”

But those allegations won’t go away when Zinke departs Washington. Nancy DiPaolo, a spokeswoman for Interior’s inspector general, declined to discuss two investigations of Zinke because they are active: “Right now, they’re going forward.”

In an interview Wednesday, Rep. Raúl M. Grijalva (D-Ariz.) — who is poised to take over as chairman of the House Natural Resources Committee in the next Congress — said even though Zinke is gone, lawmakers will continue to scrutinize how he ran the department over the past two years.

“We don’t see that as the end of it,” he said. “I think there are facts that need to come out. . . . The public’s got a right to know about some of these decisions, and who’s gaining from them."

For the 21 months of Zinke’s reign, Grijalva could only watch as Zinke killed scientific studies and weakened regulations to protect federal lands. One study by the National Academies of Science, Engineering and Medicine sought to determine the health effects faced by people who live near sites where mountaintops are blasted away to excavate coal, and another by the group sought to find ways to make working on offshore oil platforms safer.

Interior also weakened rules put in place by the Obama administration after the BP Deepwater Horizon disaster to prevent major oil spills. The Bureau of Land Management lifted regulations to allow fracking on millions of acres of protected federal lands and erased a rule curbing emissions of the most potent greenhouse gas, methane, produced by fracking operations.

Last month, the day after Thanksgiving, Interior announced it was weakening federal rules that protected sage grouse on 9 million acres of land so mining companies could work it. Sage grouse are protected not only because their historic numbers have cratered, but also because the bird’s well-being is an indication of the health of an entire ecosystem called the sagebrush, which teems with animals that are either threatened or are on the verge of endangerment.

Interior declined an interview request for this story. “The secretary is not available,” spokeswoman Heather Smith said in an email.

Zinke’s approach to running the department alienated employees. At first, Zinke said he would fight Trump’s proposal to cut a hefty percent of Interior’s budget, but he reversed himself within weeks and wholeheartedly supported the president’s plan to eliminate 4,000 jobs. “This is what a balanced budget looks like,” he told lawmakers, who ultimately voted against it.

In a speech last year to a federal advisory board dominated by oil and gas industry executives, he described Interior’s 70,000-person workforce by saying, “I got 30 percent of the crew that’s not loyal to the flag,” meaning they didn’t support Trump or his policies.

He proposed a massive and costly reorganization of his department, drafting plans to merge different divisions into geographic regions and move the Bureau of Land Management out West. He froze or dismantled dozens of Interior advisory boards, establishing new ones focused on promoting trophy hunting overseas as well as hunting on public land. And he removed senior executives seemingly on a whim, drawing a rebuke from the inspector general’s office following an investigation.

Six of seven regional directors at the National Park Service have either been reassigned or retired rather than give in to a cross-country move ordered by Zinke. One senior executive, Joel Clement, a scientist and policy expert, was reassigned to an accounting position for which he has no experience after publicly disclosing how climate change hurt Alaska Native communities. Clement quit and became a whistleblower. His reassignment is under investigation.

“You have to wonder if all of this reshuffling isn’t part of a grand plan to force out the most senior members of the service, those who know law and policy, and would likely push back on many of the unfortunate policies of this administration,” said Maureen Finnerty, chair of the Coalition to Protect America’s National Parks.

Federal data show Interior lost 500 employees between Trump’s inauguration last year and June, a 1 percent decline in the workforce. Under the Obama administration, the agency grew by 4 percent.

Democrats in Congress, as well as conservationists nationwide, called Zinke’s work an abomination, particularly for someone who said in confirmation hearings that his stewardship would be similar to Roosevelt, widely hailed as America’s greatest conservationist president. In March, Sen. Ron Wyden (D-Ore.) reminded Zinke that during his confirmation hearings, he “mentioned Teddy Roosevelt nine times.”

“I said I would support your nomination, and I did,” Wyden said. “I will tell you right now, as of today, it is one of the biggest regrets in my public service.”

Andrew Ba Tran contributed to this report.