A leading Democrat in the race for Missouri governor has come out as a staunch opponent of the Clean Power Plan, the centerpiece of President Obama's climate change agenda.

Missouri Attorney General Chris Koster is the state's shoo-in for the Democratic nomination in the right-leaning "Show Me" state. But that doesn't make him an automatic fan of the Obama administration's emissions cuts for power plants.

Koster told a group of utilities that he plans to add Missouri to the growing list of states seeking to oppose the Clean Power Plan in federal court at the end of the month, when the rule is expected to be published in the Federal Register. Observers say he had been mulling joining the lawsuit for weeks.

He said the Environmental Protection Agency's "Clean Power rule effectively eliminates Missouri's competitive advantage as a low energy-cost state." The state has faced a number of challenges from EPA regulations in the past and has been a key litigant in challenging contentious cross-state air pollution rules and an expensive rule on mercury and acid gases that caused power plants to close.

Missouri is heavily dependent of coal for its electricity. Critics of the Clean Power Plan say it would put pressure on a number of Missouri's power plants to close in favor of renewable energy development. The plan calls for states to reduce their emissions by a third by 2030.

Koster is running for governor against St. Louis-Republican Eric Greitens, a former Navy SEAL who has tried to label Koster as a green-leaning Democrat. But some political consultants say the governor's race is broader than just being Democrat or Republican when it comes to energy.

They say Missouri demonstrates an antipathy toward the Clean Power Plan and the president's climate change agenda can cross parties in an election season.

"Opposition to this carbon rule is not a partisan issue — it's a substantive one," said Liz Mair, a senior political strategist and industry consultant. It shows that the "politics of the carbon rule are bad for swing state Democrats."

Dave Robertson, a political science professor at the University of Missouri-St. Louis, told the St. Louis Post-Dispatch that Koster's announcement shouldn't be taken as a surprise. He said "as long as he is really the only candidate in a strong position to get the Democratic nomination for governor, this is almost politically risk-free for him."

Robertson said the Clean Power Plan "is not the top priority" for many Democratic voters in most parts of the country, and Missouri is no exception.

Jack Conway, the Democratic attorney general from Senate Majority Leader Mitch McConnell's home state of Kentucky, is already part of the group of states champing on the bit to sue the EPA. McConnell has been urging governors around the country not to comply with the climate rules, arguing that the EPA climate plan will drive up electricity prices and make the power grid unstable.

Opposing the plan has been a main priority for his leadership, and McConnell is expected to introduce a resolution of disapproval against the rule soon, say aides. The resolution could repeal the EPA rule, if it gains enough votes to survive a certain presidential veto.