President Obama's climate agenda has dominated the energy and environment debate for the past year. Next year, the debate will be defined by how his administration defends it against a Republican Congress.

GOP lawmakers plan an early attack against an Environmental Protection Agency proposal to regulate carbon emissions from power plants. While putting legislation on the floor to approve the Keystone XL oil pipeline will be the Senate's first order of business, incoming Majority Leader Mitch McConnell has vowed that limiting or stopping that rule is one of his top legislative priorities.

"I couldn't be angrier about it, and whatever we can think of to try to stop it, we're going to do," the Kentucky Republican told the Associated Press earlier this month, adding, "I know it won't be easy with Barack Obama in the White House."

The policy is the cornerstone of Obama's climate agenda, and it's likely to end up in the court system soon after the rule is finalized in June.

It's at the center of conservatives' beef with Obama's environmental and energy policies. But Democrats have loaded up key Senate energy and environment committees with liberals who strongly defend the proposed rule, as do Obama's environmental allies.

Fights over the proposal are expected on Capitol Hill and in capitals across the country. Groups such as the American Legislative Exchange Council, a organization that promotes conservative policies, have created model policy resolutions against the plan that members are expected to introduce in state legislatures. The industry-backed American Coalition for Clean Coal Electricity also is working with state lawmakers on challenges to the emissions rule.

Environmental groups are prepared to back up the power plant rule. Many hope to push the EPA to increase its carbon-reduction target of lowering electricity sector emissions 30 percent below 2005 levels by 2030, seeing it as a winning issue for Democrats.

"I think one important thing that is going to happen now is that because this is likely to become a flashpoint between the president and Congress this issue is going to get a lot more attention," said David Goldston, director of government affairs with the Natural Resources Defense Council. "It's going to make it a lot harder to be on the other side."

Obama will be touting the power plant rule, which is the most aggressive action the United States has taken to slow emissions of the greenhouse gases that are blamed for driving climate change, as he heads into international negotiations next December in Paris.

The United Nations-hosted talks will aim to strike an agreement to govern emissions reductions beyond 2020, and Obama has sought to position the United States as a leader. But Republicans plan to block aid for developing nations and prevent the administration from undertaking regulatory actions to meet climate targets.

Taking down the power plant proposal will be key to their efforts to block his climate change agenda. Conservatives and industry believe the EPA proposal, which is being regulated under Section 111D of the Clean Air Act, fits with their broader message that the Obama administration has engaged in regulatory overreach.

Paul Bailey, senior vice president for federal affairs and policy with the American Coalition for Clean Coal Electricity, said he envisions "111D" becoming a politically toxic term. He compared it to cap-and-trade legislation that passed the House and fizzled in the Senate in 2010, giving way to the nascent Tea Party movement that saw many GOP lawmakers who backed the bill ousted in primaries by more conservative candidates.

"The wonks were talking to each other about cap-and-trade and over time the phrase cap-and-trade became a four-letter word," Bailey said. "[The Clean Air Act's] 111D is feeling like the same thing all over again. ... That could influence some races."

Republicans in Congress will certainly try to make it so, though the Senate won't have a veto-proof majority to overturn the power plant rule. Some Republicans might even choose to back some climate change efforts.

"Not every Republican literally would vote against every legislative proposal to deal with carbon," Bailey said.

Still, conservatives and centrist Democrats will be watching for several regulations the Obama administration is expected to propose this year so that they are finished before the president leaves office.

The first would be Interior Department rules on hydraulic fracturing, or fracking, that they call duplicative.

"That will end up in legal challenge, but there may be legislative action or oversight there as well," said Matt Kellogg, tax and environmental counsel at the Independent Petroleum Association of America.

An anticipated rule that would make a controversial coal-mining method known as mountaintop removal mining more difficult will draw the ire of coal-state lawmakers. Potential oil and gas sector regulations on methane could draw heat from politicians in energy-producing states. The greenhouse gas has a climate effect nearly 30 times greater than carbon dioxide, and environmental groups say it must be regulated to curb climate change.

"Under the Clean Air Act the EPA has a clear duty to set national limits for the methane pollution that the oil and gas industry releases," said Sarah Uhl, senior program director on methane with the Clean Air Task Force. "There are no federal limits on this pollution. The oil and gas industry can release as much methane into the atmosphere as it wants."

Crashing oil prices also will attract attention as policymakers gauge whether that will affect surging U.S. production. Oil-friendly lawmakers may seek to ward off changes to federal tax policies that benefit the oil industry as independent drillers that have led the American energy boom are hurt by cheaper oil. They also will prod the Obama administration to open more federal offshore and onshore land to drilling. The White House is now drafting its next five-year offshore drilling plan.

Republicans also will try to handcuff a proposal to tighten the level of ozone, otherwise known as ground-level smog, that is allowed in the atmosphere. Public health officials say lowering the level is necessary to prevent damage to human hearts and lungs, citing the opinions of an independent panel of scientists that advises the EPA. But industry groups contend the proposal could become the most costly environmental regulation ever by making permitting and expanding refineries, factories and other big emitters more difficult.

"Ozone is at the top of the list," said Howard Feldman, director of regulatory and scientific affairs with the American Petroleum Institute.