WASHINGTON — In a Trump administration beset by lost opportunities, muddled strategies and frequent missteps in its first 100 days, one area stands out for its disciplined approach and early successes: the assault on environmental regulations.

Unlike the Affordable Care Act repeal debacle or immigration orders that are tangled in federal courts, the administration has managed in a few short months to upend numerous hard-fought environmental protections and climate actions that the fossil-fuel industries have been targeting for years.

Planned action on climate change has been shelved, national monuments are imperiled, and clean air and water rules have been eroded. Doubt has even been cast on the ability of states like California to protect their own strong environmental regulations.

The tens of thousands of protesters who converged Saturday on Washington and other cities for the People’s Climate March confronted a policy landscape that perhaps more than any other has been transformed under President Donald Trump.

Even as marchers were making their signs and plotting their chants on Friday, Trump was delivering another blow, signing an order that could open the California coast and Arctic to new oil and gas drilling.

“It has been a wrecking ball right out of the gate,” said Rep. Jared Huffman of San Rafael, D-Calif., who is on the House Natural Resources Committee. “We shouldn’t underestimate the amount of damage that has already been done to the environment by an administration that can’t seem to get almost anything else done.”

The fast pace at which the administration has eased environmental rules reflects how vulnerable many of them are after having been put into place administratively by an Obama White House that could not get consent from a hostile Congress.

But it is also a sign of the unprecedented sophistication and political organization of fossil-fuel and related industries, which have nurtured for years a network of think tanks and politicians in preparation for this moment. That team of industry-supported activists now dominates the leadership of Trump’s environmental agencies, which have set about killing those rules in the hopes of boosting some U.S. industries.

“We are very heartened by the progress that has been made,” said Myron Ebell, who headed Trump’s transition at the Environmental Protection Agency and has since returned to the Competitive Enterprise Institute, an industry-funded group that takes a lead nationally in denying mainstream climate science. “I’m not going to take credit, but one might take a look at the work of the transition for the Department of Energy, Department of Interior, and the EPA.”

The transition at each of those agencies was run by leaders from think tanks aligned with the donor network guided by fossil-fuel billionaires Charles and David Koch. The organizations over the past several years have sent lobbyists and attorneys across the country in a coordinated effort to undermine President Barack Obama’s climate action and fight state efforts to promote clean energy.

Among their most prized allies was Scott Pruitt, now the EPA administrator, who during the Obama administration developed extensive legal strategies for attacking federal environmental rules while serving as Oklahoma’s attorney general. Trump’s energy secretary, former Texas Gov. Rick Perry, oversaw a similar effort in his home state.

Business groups have praised the administration’s quick work, saying the Obama-era rules were expensive, burdensome and unnecessary.