As Americans flock to the nation’s beaches this summer, it is important to understand what Mr. Trump’s recent moves portend. Specifically, his executive order calls for the reconsideration of a critical safeguard that is the most important action the government has taken to reduce offshore drilling hazards. This safeguard, the well control rule, tightened controls on blowout preventers designed to stop explosions in undersea oil and gas wells. The rule was based in part on lessons the commission learned about the root cause of the BP disaster.

Had this common-sense rule been in place on April 20, 2010, that calamity might well have been averted. Weakening or rescinding this rule would increase the risks of offshore operations, put workers in harm’s way and imperil marine waters and coastlines.

Mr. Trump’s order also directed the Interior Department to review current rules on offshore drilling. Opening more areas to exploration, as the Trump administration moved to do last week, could threaten the fragile Arctic Ocean off Alaska as well as environmentally sensitive reaches of the Atlantic Ocean and the Gulf of Mexico. A spill in any of those waters could threaten multibillion-dollar regional economies that depend on clean oceans and coastlines.

Nothing has changed to justify these moves since the current five-year offshore leasing plan, which runs through 2022, was finalized after years of public and industry input. Broad public opposition to expanding drilling into frontier areas has not diminished. Nor are the identified potential harms to economies and ecologies any less significant.

In short, drilling in the outer continental shelf remains risky business. Safety and oversight in offshore drilling continues to need improvement, not roll backs.