In February, the Donald Trump Administration fulfilled a months’ long promise to rescind EPA’s endangerment finding—the 2009 rule underpinning federal regulation of greenhouse gas emissions—in what it dubbed “the single largest deregulatory action in U.S. history.”
In the November-December 2025 issue of the Environmental Forum, UCLA law professor Ann Carlson argued that doing so might actually give states more latitude to enforce vehicle emissions standards. If EPA says it lacks authority to regulate greenhouse gases under the Clean Air Act (CAA), then federal preemption would no longer prevent states from issuing their own climate rules, Carlson explained.
The Trump Administration, however, seems intent on making sure that doesn’t happen. On March 12, the U.S. Department of Justice (DOJ) sued California over its rules to limit carbon dioxide emissions from vehicles. The state has for decades received waivers from EPA under the CAA to set nation-leading vehicle emissions standards. In its lawsuit, DOJ argued that federal fuel efficiency standards under the Energy Policy and Conservation Act of 1975 (EPCA) preempted California’s and other state tailpipe carbon emissions rules.
But in both repealing the endangerment finding and suing California, the Trump Administration has invoked federal climate authorities that it has simultaneously negated. States cannot issue vehicle carbon emissions standards because of existing federal laws on greenhouse gases, it says. At the same time, however, federal officials have made every effort to nullify those very authorities under the CAA and EPCA.
Such contradictions could undermine the Trump Administration’s own goals to block climate action.
EPA’s final rule rescinding the endangerment finding, for example, asserted that the CAA “continues to apply by its own force to preempt state laws, regulations, and causes of action that adopt or attempt to enforce any standard relating to the control of emissions from new motor vehicles or engines.” That is, despite the Agency’s repeal of its authority to issue federal vehicle carbon emissions standards, state efforts are still preempted by that authority.
Legal scholars at Harvard Law School described the provision in the draft rule as an “attempt to simultaneously disclaim and retain regulatory power.” David Pettit at the Center for Biological Diversity described the discrepancy to E&E News as EPA wanting “to have its cake and eat it too.”
Another contradiction emerges in DOJ’s lawsuits against New York’s and Vermont’s climate Superfund laws, which seek financial compensation from oil and gas companies for climate damages. In those suits, the Trump Administration argued that the federal government’s “comprehensive program for regulating air pollutants in the United States—including greenhouse gases” under the CAA—preempted state climate laws. The New York attorney general’s office was quick to point to what it called an “inconsistency” between those arguments and EPA’s repeal of the endangerment finding.
The Administration’s lawsuit against California’s clean car rules asserts federal preemption under a different statute: national vehicle fuel economy standards under the EPCA. The challenge comes less than one year after the U.S. Congress passed resolutions to block the state from banning gas-powered cars by 2035, which President Trump subsequently signed into law.
It’s not the first time the Trump Administration has used this argument to target the Golden State’s tailpipe rules. In 2019, the National Highway Traffic Safety Administration (NHTSA) finalized a “One National Program Rule” that claimed the agency’s fuel economy standards under the EPCA preempted any state vehicle carbon emissions standard. EPA also withdrew California’s CAA waiver at that time.
But once again, the Trump Administration has undermined the same federal authority it champions. Trump’s “One Big Beautiful Bill” budget reconciliation law removed all penalties for not complying with federal fuel economy standards under the EPCA. Those standards technically only preempt state laws when they’re “in effect,” UC Berkeley law professor Dan Farber pointed out on the blog Legal Planet.
“There’s a reasonable argument that the repeal of all penalties means that the CAFE standards are no longer in effect, so neither is the prohibition on state regulation,” Farber wrote. Without enforcement of penalties, “such a regulation is as insubstantial as a ghost,” he concluded.
It’s unclear what will end up happening with the Trump Administration’s lawsuit against California’s tailpipe rule. (Legal challenges brought by environmental groups against the NHTSA’s previous “One National Program Rule” were put on pause when President Joseph Biden took office.) The elimination of the endangerment finding, on the other hand, has prompted several lawsuits and will likely end up before the U.S. Supreme Court, according to multiple legal experts.
The high court has declined to hear challenges to the endangerment finding as recently as 2023. But none of the five justices who ruled in the majority in Massachusetts v. EPA, the 2007 case establishing the Agency’s authority to regulate greenhouse gases, are still on the bench. That leaves the fate of EPA’s finding an open question.
However the courts resolve these disputes, the current approach has already reframed the terrain. By simultaneously dismantling and invoking federal authority, the Administration has introduced legal ambiguity that may invite litigation and experimentation alike. For industry, that uncertainty may complicate investment and compliance decisions. For states, it could create a costly bind—pursuing climate policy under the constant threat of preemption claims grounded in authorities the federal government itself is disavowing. The result may be not deregulation but could result in a more fragmented and contested system of climate governance.