All states already have state level equivalents of the EPA. EPA should at least be reduced to an advisory and research role with no regulating authority at all. They can recommend stuff all day long, but it will be up to the states to implement. That by itself would have immeasurable benefits.
California refuses some trade with other States if they don’t comply with their regulations. They had all trucks go through expensive overhaul, putting small truckers out of business, then told out of state truckers they couldn’t drive through their state if not in compliance.