Trump Chooses David Bernhardt, a Former Oil Lobbyist, to Head the Interior Dept.

Mr. Bernhardt was narrowly confirmed to his current post by a vote of 53 to 43, with most Democrats voting against him. He is likely to face further scrutiny in his next confirmation hearings. If enough Democrats opposed his nomination, they could block a procedural motion requiring 60 votes to bring his confirmation to the Senate floor.

Mr. Bernhardt, who was also a top interior official in the George W. Bush administration, went on to work for some of the country’s largest oil and gas companies. As a partner in the law firm Brownstein Hyatt Farber Schreck, he lobbied for the oil companies Cobalt International Energy and Samson Resources. His legal clients have included the Independent Petroleum Association of America and Halliburton Energy Services, the oil- and gas-extraction firm once led by former Vice President Dick Cheney.

In August 2017, Mr. Bernhardt signed an ethics letter saying he would recuse himself from policy decisions that might stand to benefit former clients specifically.

If confirmed, Mr. Bernhardt will lead a sprawling department that oversees the nation’s nearly 500 million acres of public land, including vast national monuments and protected wilderness areas. Already, in little more than a year as the department’s deputy, he has overseen numerous polices aimed at opening public lands and waters to mining, drilling, farming and other development.

Environmentalists see him as a threat. “David Bernhardt is the most dangerous man in America for endangered species and public lands,” said Noah Greenwald, the endangered species director at the Center for Biological Diversity, an advocacy group, adding that he “has been dismantling basic protections for lands that belong to all of us and the vulnerable species, like the sage grouse, that depend on them.”

This year, Mr. Bernhardt oversaw the revision of a program to protect tens of millions of acres of habitat of the imperiled sage grouse, a puffy-chested, chickenlike bird that roams over 10 oil-rich Western states. His proposal to change that plan, made public in December, would strip protections from about nine million acres of the sage grouse habitat, a move that would open more land to oil and gas drilling than any other single policy action by the Trump administration.

Mr. Bernhardt has also helped shepherd policies such as loosening the standards of the Endangered Species Act, speeding the path to opening the Arctic National Wildlife Refuge to new oil and gas drilling, and reducing the boundaries of national monuments to open the land to mining and drilling.