Sen. Jay Rockefeller was an exception to the roster of coal country lawmakers who lined up Wednesday morning behind a GOP push to derail an Obama administration rule targeting mercury emissions from coal-fired power plants.

The five-term West Virginia Democrat broke sharply from his congressional delegation to oppose an attempt by Sen. Jim Inhofe (R-Okla.) to block a controversial EPA mercury rule — a political risk in a state that has grown increasingly isolated from President Barack Obama and his environmental policies.