The flurry of announcements from Trump's Environmental Protection Agency aligns with the president's vows to slash regulations to boost industries from coal to manufacturing, and ramp up the nation's oil and minerals production.
But they are also destined to weaken core environmental protections imposed by past presidencies to protect air and water quality and fight fossil fuel-driven climate change.
"Today is the most consequential day of deregulation in American history," EPA Administrator Lee Zeldin said in a video message posted on X.
In total, his agency announced more than 30 deregulatory measures in a dizzying succession of separate press releases.
Zeldin started the day by announcing, alongside Republican politicians and the American Farm Bureau, that he will narrow the definition of waterways that receive protection under the Clean Water Act - in a move that could ease limits on runoff pollution from agriculture, mining, and petrochemicals.
The agency later said it would review the Biden-era clean power plant rule that seeks to reduce carbon emissions from power plants to fight global warming and would also roll back greenhouse gas emissions standards for heavy- and light-duty vehicles for model year 2027 and later.
The power and transport industries together make up around half of the nation's greenhouse gas emissions, and were vital targets in former president Joe Biden's efforts to slow climate change.
The agency also said it will take steps to undo a key scientific finding from 2009 that greenhouse gas emissions endanger public health, a provision that forms the bedrock of all of the EPA's greenhouse-gas regulations so far.
The so-called "endangerment finding" came as a result of a Supreme Court ruling in the 2007 Massachusetts v. EPA case that greenhouse gases are covered by the Clean Air Act.
The EPA under former president Barack Obama finalised the finding in 2009, and the 2022 Inflation Reduction Act - Joe Biden's signature climate law - codified language deeming greenhouse gases are air pollutants.
Environmental groups said they will fight rollback.
"This move won't stand up in court. We're going to fight it every step of the way," said Jason Rylander, legal director at the Centre for Biological Diversity's Climate Law Institute.
The National Mining Association, which represents some coal miners, applauded the rollback of the clean power plant rule, saying it was "long overdue" as data centres and AI have driven demand for power.
In addition to greenhouse gas regulations, the Trump administration plans to roll back other air and water regulations that have been in place for decades for the power industry.
The American Exploration & Production Council applauded the flurry of deregulatory moves.
"AXPC has long called for modifications to several EPA-administered rules so that they are workable, effective, and build on the significant emissions reductions made by American independent producers of oil and natural gas," AXPC CEO Anne Bradbury said.
Trump's EPA said it will reconsider mercury and air toxics rules that had been updated under Biden that it says were designed to target coal-fired power plants. It said it would shift the regulation of coal ash from power plants, which contain heavy metals and other chemicals, to states.
It also said it plans to revisit standards set under the Biden administration to reduce soot and air particulate matter standards set under Biden.
The EPA also announced measures that would dial back regulations for the oil and gas industry, including required reporting of methane emissions from oil and gas infrastructure, which had support from some major oil companies but faced opposition from smaller producers.
