In just two years, President Trump has unleashed a regulatory rollback, lobbied for and cheered on by industry, with little parallel in the past half-century. Mr. Trump enthusiastically promotes the changes as creating jobs, freeing business from the shackles of government and helping the economy grow.

The trade-offs, while often out of public view, are real — frighteningly so, for some people — imperiling progress in cleaning up the air we breathe and the water we drink, and in some cases upending the very relationship with the environment around us.

Since Mr. Trump took office, his approach on the environment has been to neutralize the most rigorous Obama-era restrictions, nearly 80 of which have been blocked, delayed or targeted for repeal, according to an analysis of data by The New York Times.

With this running start, Mr. Trump is already on track to leave an indelible mark on the American landscape, even with a decline in some major pollutants from the ever-shrinking coal industry.