President Trump’s Environmental Protection Agency recently released a proposal that would undermine not only current regulations, but regulatory efforts in the future by disavowing the legal justification for a major rule limiting mercury emissions. The proposal hinges on some wonky legalisms, but if the approach survives the expected court challenges, it could lead to a fundamental change in how regulatory impacts are measured and make it significantly harder to protect the health and safety of Americans.

The proposal at issue focuses on the amount of mercury that power plants can release as a byproduct of burning coal. Since the Reagan administration, federal agencies have used cost-benefit analyses as they weighed the consequences of proposed regulations. After years of legal wrangling, the Obama administration determined in April 2016 that it was “appropriate and necessary” to regulate mercury emissions, and that the EPA should take costs and both direct and indirect benefits (or “co-benefits”) into account when setting the limits.

The cost of cutting the mercury emissions was put at $9.6 billion, while the direct public health benefits were estimated at $6 million. But when the co-benefits from reduced soot, nitrous oxide and related emissions were added in, the estimated public health benefit ranged from $37 billion to $90 billion.

Those benefits included a reduction in health costs, a drop in lost workdays and the avoidance of as many as 11,000 premature deaths (some 4,700 heart attacks would be prevented). Clearly the broad benefits from eliminating mercury exceeded the costs that the industry faced in doing so.