type: timeline_event
On March 19, 2026, a coalition of 24 states, 10 cities, and 5 counties filed suit in the D.C. Circuit Court of Appeals challenging the Trump EPA's repeal of the 2009 endangerment finding — the foundational scientific determination that greenhouse gas emissions endanger public health and welfare. The lawsuit represented the second major legal challenge to the repeal and the largest coalition of government plaintiffs assembled against the administration's environmental agenda.
The coalition was led by New York Attorney General Letitia James, joined by attorneys general from Massachusetts, California, Connecticut, and 20 additional states. Their petition argued that the EPA had acted arbitrarily and capriciously by disregarding decades of scientific evidence, ignoring the agency's own prior findings, and failing to provide a reasoned explanation for reversing a determination that had survived multiple rounds of judicial review. The repeal had eliminated the legal foundation for all federal greenhouse gas emission standards for cars and trucks, effectively removing the federal government from vehicle emissions regulation.
The endangerment finding, originally issued under the Obama administration in response to the Supreme Court's 2007 ruling in Massachusetts v. EPA, had been the legal prerequisite for all subsequent federal regulation of greenhouse gas emissions from motor vehicles. Its repeal was the Trump administration's most consequential single action on climate policy — more far-reaching than any individual regulatory rollback because it removed the legal basis on which an entire architecture of emissions standards had been built.
Legal experts noted that the case would likely turn on whether courts applied a deferential standard to the EPA's scientific judgment or scrutinized the agency's reasoning more closely given the overwhelming scientific consensus on climate change. The D.C. Circuit had upheld the original endangerment finding in 2012, and petitioners argued that the underlying science had only grown stronger in the intervening years. The case was expected to move on an expedited timeline given the ongoing environmental consequences of the regulatory vacuum created by the repeal.