Self-described "ass-kicking, motorcycle-riding, Texas Democrat" MJ Hegar, a candidate for Texas’ deep-red 31st District, has a novel approach to environmental politics: she doesn’t care if her supporters believe in man-made climate change, but says it's hard to deny the corrupting effects of petroleum dependence on American foreign policy.

"Our dependence on foreign oil is just so damaging to our country on so many levels," Hegar told ABC News in a June interview. "I respect other people’s freedom to be discerning and to make their own decisions. But they can’t deny that the U.S. military pays the price for our dependence on foreign oil – that our diplomacy and foreign policy is complicated by our dependence."

Hegar is one of a number of progressive veterans running for Congress who have made climate change action a key part of their platforms.

"I don’t think another country, or another entity, like OPEC, should be able to have such an impact on our economy," she said.

An Air Force veteran who received a Purple Heart for wounds sustained in combat and led a 2012 fight to overturn a policy barring women from direct ground combat, Hegar is challenging Rep. John Carter, a Tea Party Republican who has held his seat for 15 years.

She sees her military background as compatible with many traditionally progressive causes: for Hegar, a robust defense strategy includes opposing travel bans, gaining independence from foreign oil, and support for environmental legislation.

In December, issuing his first major update to U.S. National Security strategy, President Donald Trump omitted climate change from the list of recognized national security threats, reversing the Pentagon consensus to define climate change as a security risk.

Candidates across the country are pushing back on that notion, by not only stressing environmental concerns like the upsurge in natural disasters, but by describing climate change as a national security threat and foreign policy issue, as well as an arena for potential economic leadership.

Maura Sullivan, a former U.S. Marine officer in the Iraq War and Department of Veterans Affairs official in the Obama administration, is the Democratic candidate for New Hampshire’s 1st Congressional District. Sullivan describes her growing worry over numerous environmental threats to national security, from displaced refugees in developing countries, to rising sea levels that could damage billions of dollars of U.S. military equipment.

"We face the potential for water shortage and famine -- something we’ve seen the United States military respond to around the globe," she told ABC News. "Our ability to respond to these crises is also significantly impaired by the threat of climate change itself. We’ve got billions of dollars of coastal assets, bases, that rising sea levels threaten."

Sullivan referenced Obama-era reports by military officials and security experts that commonly described climate change as a "threat multiplier."

In 2014, for instance, the Defense Department’s Quadrennial Review cited "threat multiplier" effects, arguing that the pressures of climate change "will aggravate stressors abroad such as poverty, environmental degradation, political instability, and social tensions – conditions that can enable terrorist activity and other forms of violence."

Like Hegar, Sullivan saw the devastating effects of oil dependency firsthand during her time in the military -- in particular, while serving as an operations and logistics officer in Iraq. She pointed out that over 3,000 American service members were killed in fuel supply convoys between 2003 and 2007 in Iraq and Afghanistan.

"A part of that is just purely caused by a dependence on oil. And, if we had a stored a replenishable energy source ... there would simply be need for fewer convoys, and that saves thousands of American lives," Sullivan said.

In Wisconsin, Randy "Ironstache" Bryce is the candidate vying for House Speaker Paul Ryan’s old seat in the 1st Congressional District. If he wins, he would flip the southeastern district blue after two decades of conservative control. He faces Bryan Steil, an attorney and former staffer for Ryan, whose website does not include any mention of climate change.

Bryce is among the most vocal candidates in 2018 on the urgency of climate action -- he has built his campaign around a "Green New Deal" plan for environmentally sustainable jobs that pay a living wage. An army veteran, he told ABC News his time in the military convinced him that the threat of climate change extends beyond extreme weather and rising temperatures.

"As a result of being dependent on fossil fuels ... we send troops to protect resources like oil," Bryce said, citing the Iraq war as an example of why the U.S. must invest in independent, renewable energy sources.

Bryce is a member of Ironworkers Local 8 Union, and has firsthand experience working in the energy industry. He argued that environmentally sustainable development is often much better for construction workers’ health and safety.

Describing his work in iron ore mining, Bryce said that after he finished each 12-hour shift, he would be "covered with red, everywhere." It took him three showers to get the red dust off his body, he said, and even then, he felt the toll the work took on his health.

"It’s just filthy. When you get done working, you’re coughing -- I stopped smoking, but I felt like I smoked a carton after every shift. And that’s with the safety equipment on, too, with the respirators," he said. "When you compare that to something like putting up a wind turbine, it's completely the opposite -- you’re tired from the work, and sometimes dirty, but it’s a clean dirt."

In addition to creating green jobs that offer workers a higher standard of living, Bryce wants to hold polluters accountable, including by prosecuting Exxon Mobil for the negative health effects of fossil fuels on the public.

Asked why he is calling to prosecute Exxon Mobil, Bryce didn’t equivocate.

"We have records that show that they knew about the negative effects of fossil fuels on the health of the public, both long and short term, and intentionally just continued profiting off it. We need to make them accountable to the communities that have been hurt by their pipelines and pollution," he said.

Exxon Mobil did not immediately respond to ABC News' request for comment on Bryce's claims.

Bryce’s "Green New Deal" stimulus aims to get the U.S. entirely off fossil fuels by 2035 while creating thousands of new jobs in the renewable energy sector.

Proponents of a "Green New Deal" -- which is also touted by democratic-socialist insurgent Alexandria Ocasio-Cortez –- say that a radical strategy for economic and environmental overhaul is the only plan commensurate with tackling the threat of climate change.

Many left-wing environmentalists argue that moderate concessions -- from the straw ban to plastic bag taxes and cap-and-trade programs –- are short-term remedies that don’t begin to address the scale of the crisis.

Climate change isn't irreversible, but if we wait any longer, it could be. We need leaders who will stop this crisis. We need to pass the OFF Act, which will transition the US to 100% green energy by 2035, and create new, good paying jobs in the process.https://t.co/swdEdTcgwf — Randy Bryce (@IronStache) August 12, 2018

One recent study from the National Academy of Sciences, dubbed the "Hothouse Earth" report, gained attention for its grim assessment of impending catastrophe. Researchers argued that only a rapid response to climate change that includes political and economic reforms stands a chance of averting crisis.

"Incremental linear changes to the present socio-economic system are not enough to stabilize the Earth System," the researchers wrote, insisting that "widespread, rapid, and fundamental transformations" in political economy are necessary to stave off disastrous outcomes.

Amy McGrath in Kentucky and Mikie Sherrill in New Jersey are two more Air Force veterans running for Congress pitching climate change as a key plank in their national security platforms.

On her campaign website, Sherrill denounces the "false choice between creating jobs, fighting climate change, and keeping our air and water clean," framing environmental concerns instead as an "economic and national security issue" that will particularly impact citizens of New Jersey, who live along 130 miles of coastline.

Meanwhile, in Kentucky -- a state with an economy fueled by the coal industry -- McGrath does not mince words in her description of environmental threats.

"A changing climate has had and will continue to have hugely disruptive effects not only on the environment, but also on migration patterns, economies, disease vectors, and political unrest around the world," her climate change platform reads. "In the 20th century, we fought wars over values or economic conflicts; in the 21st century, it will be over food, water and resources."

Climate change isn't irreversible, but if we wait any longer, it could be. We need leaders who will stop this crisis. We need to pass the OFF Act, which will transition the US to 100% green energy by 2035, and create new, good paying jobs in the process.https://t.co/swdEdTcgwf

One recent study from the National Academy of Sciences, dubbed the "Hothouse Earth" report, gained attention for its grim assessment of impending catastrophe. Researchers argued that only a rapid response to climate change that includes political and economic reforms stands a chance of averting crisis.

"Incremental linear changes to the present socio-economic system are not enough to stabilize the Earth System," the researchers wrote, insisting that "widespread, rapid, and fundamental transformations" in political economy are necessary to stave off disastrous outcomes.

Amy McGrath in Kentucky and Mikie Sherrill in New Jersey are two more Air Force veterans running for Congress pitching climate change as a key plank in their national security platforms.

On her campaign website, Sherrill denounces the "false choice between creating jobs, fighting climate change, and keeping our air and water clean," framing environmental concerns instead as an "economic and national security issue" that will particularly impact citizens of New Jersey, who live along 130 miles of coastline.

Meanwhile, in Kentucky -- a state with an economy fueled by the coal industry -- McGrath does not mince words in her description of environmental threats.

"A changing climate has had and will continue to have hugely disruptive effects not only on the environment, but also on migration patterns, economies, disease vectors, and political unrest around the world," her climate change platform reads. "In the 20th century, we fought wars over values or economic conflicts; in the 21st century, it will be over food, water and resources."