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Wh en the Trump administration laid out a plan this year that would eventually allow cars to emit more pollution, automakers, the obvious winners from the proposal, balked. The changes, they said, went too far even for them.

But it turns out that there was a hidden beneficiary of the plan that was pushing for the changes all along: the nation’s oil industry.

In Congress, on Facebook and in statehouses nationwide, Marathon Petroleum, the country’s largest refiner, worked with powerful oil-industry groups and a conservative policy network financed by the billionaire industrialist Charles G. Koch to run a stealth campaign to roll back car emissions standards, a New York Times investigation has found.

The campaign’s main argument for significantly easing fuel efficiency standards — that the United States is so awash in oil it no longer needs to worry about energy conservation — clashed with decades of federal energy and environmental policy.