WASHINGTON — He is a Democrat in a marquee Senate race, pressed by a strong Republican in a state with a challenging political environment. So when a new proposal to limit power plant emissions was seen as posing a threat to allies of the Obama administration, Senator Mark Udall of Colorado acted quickly: He embraced the plan.
“Coloradans have seen firsthand the harmful effects of climate change, including severe drought, record wildfires and reduced snowpack,” Mr. Udall said in a statement shortly after the Environmental Protection Agency plan was made public last week. “The E.P.A.’s draft rule is a good start, and I will fight to ensure it complements the work we have already done in Colorado and provides states the flexibility they need to make it successful.”
The E.P.A. proposal to reduce carbon pollution from power plants was deemed a political gift from the Obama administration to Republicans running for Senate seats in the coal-producing states of Kentucky and West Virginia, and an anchor around the necks of their Democratic opponents. Elsewhere, the threat of higher electricity bills and Republican attacks about another federal power grab were supposed to send Democrats scurrying for cover and distance from the White House.
But Mr. Udall’s example shows that not all Democrats look at it that way.
In Iowa, Representative Bruce Braley, the Democratic Senate nominee, has adopted the same approach as Mr. Udall. “Reducing our carbon output is not only necessary for the health of the planet, it’s an opportunity to continue to improve the health of the Iowa economy — which is and will remain my No. 1 priority,” Mr. Braley said.
In other states with competitive Senate races, such as Michigan, Democrats say growing public support for action to curb climate change — coupled with pronouncements by Republican candidates that human activity is not contributing to it, or their denials that the world is growing warmer — could help Democrats this year. They say it will definitely make the party stronger heading into the 2016 presidential election.
“Denying the existence of climate change is proving to be a problem for many Republicans right now, and certainly a long-term albatross for the party,” said Matt Canter, the deputy executive director of the Democratic Senatorial Campaign Committee. “Republican efforts to squeeze political gain out of this have fallen short.”
Republicans scoff at that notion. They say the new proposal has given Republican Senate contenders in Kentucky and West Virginia a huge advantage despite concerted efforts by Democrats there to distance themselves from the president and his plan. Republicans say it has also provided a handicap for Democrats running in energy-supplying states, including Alaska, Colorado, Louisiana and Virginia.
“Five months prior to the most difficult election of their careers, President Obama is turning a blind eye and a deaf ear to their concerns,” the National Republican Senatorial Committee said in a statement. “An uphill climb just got even more difficult.”
But Democrats say that public polling shows broad acceptance of the need to combat climate change and that some recent surveys show large majorities support the idea of emission limits on power plants.
“Democrats will welcome the opportunity to use this to talk about the Republicans’ dependence on oil company interests and other special interests that oppose carbon regulation for the sake of their own profits,” said Geoff Garin, a Democratic pollster who conducted a survey in Virginia this week for an environmental group.
In Colorado, which produces both fossil fuels and renewable energy, the political dynamic is much different from the one in coal states. Colorado has moved ahead with its own emissions standards, and Mr. Udall’s Republican opponent, Representative Cory Gardner, voted for a plan similar to the federal proposal while serving in the state legislature.
“In 2010, Democrats and Republicans in the state worked together knowing that any product we produced would meet Colorado’s needs far better than any unelected E.P.A. bureaucrat’s plan,” Mr. Gardner said in a statement.
The fight in Colorado is more likely to be about hydraulic fracturing, or fracking, for natural gas, and Mr. Gardner has focused on pressuring Mr. Udall over efforts to impose local government restrictions on the process.
The idea that Democrats in swing states outside the coal belt can capitalize on the emissions rules still seems a difficult proposition to some analysts. Stuart Rothenberg, the editor of the nonpartisan Rothenberg Political Report, said the new E.P.A. proposal could be joined in the minds of voters with turmoil in the administration over the Department of Veterans Affairs and the release of Sgt. Bowe Bergdahl from Taliban custody.
“How can voters not start to think that this election is a way to protest what he has done?” Mr. Rothenberg said of the president. “To the extent it is about the president, it cannot help Democrats.”
At the White House, the politics of the carbon rule is a no-brainer, officials said. In the months leading up to the announcement, Mr. Obama’s top political advisers were united in agreement that the environmental proposal would be a winner for Democrats almost everywhere but in coal country.
White House officials and other Democratic strategists say that climate change issues — and Mr. Obama’s decision to push the pollution debate to center stage — will have even greater benefits for Democrats in presidential campaigns and future congressional elections.
In interviews, they said the climate issue has become a way for voters to judge a candidate’s character and broader outlook on the world. Officials compared the issue to the growing acceptance of same-sex marriage, especially among young people and suburban women.
The president’s political advisers said that candidates who opposed regulations on pollution or denied that climate change was real were likely to be seen by those voters as ideologically rigid and unwilling to accept scientists’ conclusions. That will hurt Republican efforts to expand their support among young people and women, White House officials said.
The effort to brand Republicans as anti-science or supporters of companies that produce the most pollution has become easier, officials said, because the party has moved away from acceptance of climate change and climate regulations. Some Republicans have sought recently to soften the way they talk about the issue, saying they believe in climate change but do not attribute it to human action.
Still, as recently as five years ago, leading Republican politicians embraced so-called cap-and-trade regulations; now, the party’s leadership vigorously opposes them.
Mr. Garin, the pollster, said the hardening opposition among many Republicans to the science of climate change threatens to undermine their efforts to win back the White House in 2016.
“The Republicans have created a negative branding around the perception that it is a backward-looking party,” he said. “That perception gets deepened by their rejection of climate science.”
White House officials point to two examples as evidence of the problem for Republicans — and the potential opportunity for Democrats.
In 2010, when the recession was near its worst and Republican fortunes were on the rise, voters in California easily defeated a proposal that would have suspended the state’s aggressive air pollution laws until the economic struggles were over.
And in 2013, Terry McAuliffe, then the Democratic nominee for governor in Virginia, ran television ads attacking his Republican opponent for denying the existence of climate change. Mr. McAuliffe won.