The ideological divide over climate change widened this week in the Senate committee charged with shaping America's energy policy, setting the stage for a partisan showdown over the new Republican majority's plans to attack the Environmental Protection Agency, build the Keystone XL pipeline and drive fossil fuel expansion.

Democrats' replacement of three pro-fossil-fuel lawmakers with more pro-climate-action senators means that any across-the-aisle cooperation on the Senate Energy and Natural Resources Committee is probably dead, according to political strategists. While Republicans will control the panel 12-10 in 2015, Democrats could delay—or even potentially derail—the GOP's pro-fossil-fuels agenda by nitpicking bills during committee mark-up or by threatening a presidential veto.

"The GOP's appointments are evidence of the increasing desire within the party to roll back Environmental Protection Agency regulations," said Ford O'Connell, a Republican strategist who served as an adviser on the 2008 McCain-Palin presidential campaign. "The Democrats' decisions were definitely calculated, defensive choices. They chose three of their strongest environmentalists...There will be some serious battles in the next two years."

David Goldston, a political strategy expert and director of government affairs for the Natural Resources Defense Council, said he wasn't convinced the Democrats' choices were deliberate. Rather, they could simply represent the widening divide between the parties' stances on climate issues.

"My guess is that if you just assigned people randomly, you'd sort of have the same ideological pattern, given the make-up of this Congress," he told InsideClimate News.

New Committee Lineups

Republicans named to the committee four newly elected senators who represent fossil fuel-driven electorates: Bill Cassidy of Louisiana, Cory Gardner of Colorado, Steve Daines of Montana and Shelley Moore Capito of West Virginia. All four promised in their campaigns to fight for President Obama's climate action agenda, particularly the Environmental Protection Agency's strategy for regulating greenhouse gas emissions, known as the Clean Power Plan. Together, they pulled in more than $2.6 million in campaign contributions from oil and gas interests in 2014, according to the Center for Responsive Politics, a nonpartisan group that tracks election finance.

The Democrats' new energy committee members are Senators Mazie Hirono of Hawaii, Independent Angus King of Maine, who typically caucuses with the Democrats, and Elizabeth Warren of Massachusetts. Former Democrat committee members Brian Schatz of Hawaii and Tammy Baldwin of Wisconsin were reassigned to other panels and their seats not refilled as a result of the party losing its majority in the election.

The GOP made it clear after the November elections that President Barack Obama's climate strategy was one of the party's key targets for 2015. The Republican-led Energy and Natural Resources Committee will work alongside the Environment and Public Works Committee to produce legislation to dismantle many of the White House's programs. The Senate's most vocal climate denier, Jim Inhofe of Oklahoma, will probably lead the environment and public works panel.

At the top of the agenda will be introducing legislation similar to a bill that failed in November to fast-track a decision on the controversial Keystone XL pipeline, which would send 830,000 barrels a day of carbon-heavy tar sands oil from Alberta to Texas.

The GOP sees implementing its pro-fossil-fuels strategy as an important step toward winning the presidency in 2016. The party recognizes it needs to prove to voters that it can effectively govern. The Republicans also know they need to win the support of moderate, blue collar, middle class Americans. Party leaders hope they'll be able to accomplish both by expanding oil and gas industry jobs.

What happens in the Senate Energy Committee, as well as the Environment and Public Works Committee, will have a "direct and immediate effect" on the success of the party moving forward, O'Connell said.

If the Democrats are able to stall this strategy, they may be able to show voters that a Republican-led government isn't effective and doesn't create jobs—the strategy the GOP used this year, in reverse.

Out with the Old, In with the New

The outgoing chairwoman of the Energy and Natural Resources Committee is Sen. Mary Landrieu of Louisiana, a staunch supporter of fossil fuels who was almost always among the top recipients of oil and gas-industry campaign donations during her 18 years in Congress. She had a 51 percent pro-environment score from the League of Conservation Voters, a political advocacy organization that tracks lawmakers' votes. Landrieu lost her re-election bid to Cassidy in a December runoff.

"It is no secret that climate-oriented Democrats were not heartbroken to see her lose," said R.L. Miller, chair of the California Democratic Party's environmental caucus and founder of Climate Hawks Vote, a super PAC that helps elect climate-conscious candidates.

Sen. Tim Johnson of South Dakota, who retired this year, cast some key pro-climate votes during his final weeks, including voting against the Keystone XL fast-track proposal in November. He also supported expanding renewable energy. For the most part, though, Johnson backed expanded oil and gas drilling in the U.S. He had a 72 percent pro-environment score from the LCV.

Sen. Mark Udall from Colorado, who was unseated by Gardner, was the most climate-conscious of the Democrats ousted from the committee this year, with a League of Conservation Voters pro-environment score of 97 percent. However, Udall's pro-fracking stance frustrated environmental and climate leaders. He also largely avoided giving his opinion on the Keystone XL, though he did join Johnson in voting against the November bill.

Landrieu, Johnson and Udall's replacements generally have much stronger pro-environment voting records. Warren, a potential presidential candidate, hasn't focused on energy and environmental issues in the past, but climate advocates said they hope her progressive background will make her a formidable opponent to the GOP's anti-climate-action committee members.

"I don't see Warren as someone who would compromise when it comes to climate change," Miller said.