West Virginia Attorney General Patrick Morrisey is stepping down as chairman of the national organization of Republican attorneys general.
Morrisey, re-elected last year to a second term, has launched a campaign for the U.S. Senate.
The association and Morrisey were involved in challenges to federal regulations under the Obama administration, including the plan to lower carbon emissions from power plants.
Its political action committee bought almost $6.8 million in ads promoting Morrisey for a second term and attacking his opponents, outspending each.
The association says Arkansas Attorney General Leslie Rutledge will succeed him.