WHITEFISH, Mont. — When Interior Secretary Ryan Zinke was a state senator from this idyllic mountain town, he drove a Prius, sported a beard and pushed President Barack Obama to make clean energy a priority.

Today, the beard and Prius are gone, and Mr. Zinke has emerged as a leading figure, along with Scott Pruitt of the Environmental Protection Agency, in the environmental rollbacks that have endeared President Trump to the fossil fuel industry and outraged conservationists.

In the last year, Mr. Zinke has torn up Obama-era rules related to oil, gas and mineral extraction and overseen the largest reduction of federal land protection in the nation’s history, including an effort to slash the size of Bears Ears National Monument.

But here in Montana, where support for drilling in certain beloved areas can be a career killer, Mr. Zinke has struck a different note. And as he faces allegations that he has violated travel and ethics rules, an examination of his Interior Department record shows that his pro-development bent has not always applied to his home state, where he is viewed as a fiercely ambitious candidate for future office.