The last time Congress made a serious effort on climate change, Joe Manchin campaigned for a Senate seat in West Virginia by shooting a rifle at a cap-and-trade bill. And Manchin, who won, is a Democrat.

Four years on, Republican candidates who deny the existence of climate change may be shooting themselves in the foot – and Democrats might even be able to say the words "global warming" out loud on the campaign trail between now and November.

The rules being announced by the Environmental Protection Agency on Monday represent a workaround – President Obama had to circumvent Congress and use his executive authority to enact the EPA's new regulations on power plants. But they also mark a sea change on sea-level rise: in a year when big money and big policy changes have made climate change a legitimate mid-term election issue, it's no longer political poison to talk about the threat to the planet. In 2014, it may even be a plus for some candidates trying to save it.

As it turns out, the political climate is changing. Two-thirds of Americans supported strict carbon rules for power plants. Heat waves, Arctic winters, drought, wildfires, hurricanes, storm surges, even a rise in hay fever - these have made climate change personal to many Americans, and the conventional wisdom no longer holds. West Virginia is West Virginia – a coal state where guns and the pro-coal crowd tend to win, and talking green doesn't – but some strategists even see climate change as part of a winning Democratic brand headed all the way to 2016.

"I think we own this," outgoing White House press secretary Jay Carney said of the sleeper issue of this election year. And like all election issues these days, somebody tries to help buy ownership.

It's no coincidence that Senate majority leader Harry Reid's favorite targets are the conservative oil billionaire Koch brothers – all the better for attacking Republicans as anti-science, and beholden to industry and conservative groups.

Others are also speaking up, too, encouraged by an infusion of $100m from the billionaire environmentalist Tom Steyer for pro-climate candidates in seven Senate and gubernatorial races.

In Michigan, Steyer is supporting Democrat Gary Peters against Republican Terri Lynn Land, who says she does not agree with "radical liberals" about the causes of climate change, and that there should be a debate as to whether or not it is real. Peters warns the Great Lakes are in danger because of global warming, he has protested against pet coke dumps along the Detroit river, and he opposes the Keystone XL pipeline – a decision on which the administration has put off until after November, not that it's going anywhere as part of the conversation.

Steyer is also supporting Jeanne Shaheen, who is trying to hold her New Hampshire Senate seat – and who argues Americans have a "moral obligation" to deal with climate change.

Others are out in front on climate change, even without encouragement from billionaire campaign contributers. Don Beyer, a car dealer running for a House seat in northern Virginia, sent out direct mail and bought television ads calling for a carbon tax – a position that not too long ago would have been seen as political suicide.

Of course, Democrats fighting in oil states like Alaska or Arkansas rarely, if ever, mention climate change or Keystone. Senator Mary Landrieu may actually be losing mega-donor support in her razor-close Louisiana re-election bid because of her pro-Keystone, anti-EPA positions.

But there are growing signs that scientific truth may beat out political fear.

Even in red-state Georgia, the Democratic Senate candidate, Michelle Nunn, has no time for climate deniers: "The science is clear," her campaign website says. And when the campaign chair for one of her potential opponents does something like go on Facebook during last winter's epic ice storm with a post beginning "Hey Atlanta! Quit whining...", Democrats start to realize it's just bad politics to ignore the environment when it affects so many people.

A lot of this country is already moving away from coal - to natural gas, wind and solar. Iowa, where Tuesday's Senate primary is hinging on climate legislation, gets more than 25% of its electricity from wind power. Kansas gets about 20%. Texas, North Dakota and other states are profiting from the oil and natural gas boom. All of those states can come out winners with the EPA's new power plant rules.

A poll for the Natural Resources Defense Council (NRDC) Action Fund of nine battleground states – Arkansas, Alaska, Colorado, Iowa, Louisiana, Michigan, New Hampshire, North Carolina and Virginia – found 53% support for the carbon pollution controls, even among red-state Republicans.

"Climate denial will not last," Heather Taylor-Miesle, who directs the NRDC action fund, said last week.

And she might be right already. Climate deniers remain in the majority among Republicans in Congress, but even they're beginning to dial it down. Marco Rubio, whose home state of Florida will be swamped by sea-level rise, was forced last month to backpedal on his denial, and House speaker John Boehner said last week he is "not qualified" to debate climate science.

If all unfolds according to Obama's plan, the EPA rules will be final by mid-2016, just in time for the next presidential election. By then, any Republican eyeing a run for the White House is going to have to face up to the facts, Taylor-Miesle insists.

"I don't believe a person can win the White House in 2016 that is a climate denier," she said. "I just don't."