This month the Trump administration officially announced its intention to withdraw from the Paris climate accord, a decision that is out of step with the American people. Instead it’s one in a long series of rear-guard actions aimed at preventing the government from addressing the climate crisis.

These efforts by conservatives have become more desperate as the quality of data available to earth scientists has improved and begun to shift popular opinion. Whereas in 2001, the Intergovernmental Panel on Climate Change (IPCC) found a 67 to 90 percent chance that greenhouse gas emissions were responsible for global warming, this confidence has now risen above 95 percent. This mounting confidence has slowly convinced Americans, with two-thirds believing that climate change is caused by human activity.

One reason environmentalists currently enjoy the benefits of scientific certainty dates back to an early victory in the climate wars, the battle to gain approval for the Earth Observing System (EOS). The story of that victory makes clear that conservatives have been opposed to understanding and addressing global warming for decades, and underscores that although moderate Republicans once provided critical support for earth science research, their decline means that taking action on climate is going to require Democratic victories in 2020.

In the 1980s, NASA began studying a Mission to Planet Earth (MTPE) that would focus on developing a scientific understanding of Earth to enable improved prediction of climate, weather and natural hazards. When he took office, President George H.W. Bush adopted the idea as a key presidential initiative and gained initial approval for a 10-year, $17 billion program. Despite Bush’s support, many congressional Republicans believed global warming was, in the words of then-Rep. Bob Walker (R-Pa.) “too narrow [a problem] for the sort of money we’re investing.” They began organizing to kill the project, which forced NASA to restructure MTPE/EOS several times in the face of steady budget cuts.

After Republicans swept into power in both chambers of Congress in 1994, many believed the time had come to fully eliminate the program. Walker, the new chair of the House Science and Technology Committee, was their point person. He requested a review of the program and challenged whether “the science that is being conducted as part of the MTPE/EOS program [was] fully justified on strictly scientific terms?” This was a classic strategy at the outset of the Republican War on Science, attempting to cast doubt on sound science. MTPE Director Charles Kennel recalled that “The warning was unmistakable: make sure that you don’t go out on a limb on [this] issue.”

Then Walker used the House Budget Committee to target MTPE/EOS. He urged that the initiative’s budget, which had already been reduced to $8 billion, be slashed by another $5 billion.

NASA condemned the resulting budget resolution, arguing that it would effectively kill MTPE/EOS. NASA Administrator Dan Goldin decried how it would destroy EOS’s basic feature — comprehensiveness. More important, he said, “It would condemn American scientists to pursuing an approach to environmental research that is more than a decade out of date.”

Of course, this was exactly the point. Conservative Republicans didn’t want EOS to provide climate scientists with reams of data to steadily increase the fidelity of their predictive models. Fossil fuel companies were already funding a disinformation campaign to sow doubt within the American electorate, and their allies in Congress didn’t want an expensive government program to collect solid scientific evidence regarding the likely impacts of global warming.

As House Republicans’ assault on EOS continued, the scientific community maneuvered to save the program by appealing to Senate moderates and more environmentally conscious conservatives of one stripe or another. They were targeting members like Sen. Conrad Burns (R-Mont.), who while he leaned right, argued that “the program will easily pay for itself in lives and property saved and improved water management.” It was easier to find Republican senators willing to consider MTPE because the chamber wasn’t as far along in the turn toward radicalism that would ultimately characterize most congressional conservatives.

Scientific luminaries urged NASA to abandon its reliance on large orbital platforms in favor of smaller, more nimble satellites. They also advocated for a revised EOS mission focused on collecting data to improve studies of atmospheric ozone, seasonal to interannual climate change, long-term climate variability and land-cover change and global productivity — each objective consistent with international priorities. When Goldin and Kennel accepted these recommendations, NASA had essentially transformed an expensive hardware development project into something more affordable — roughly 30 percent less costly — making Republican complaints about a bloated budget moot.

The scientific assessment that Walker requested also backfired on conservatives. The final report extolled NASA’s new plans for MTPE/EOS and lauded the program’s ability to contribute to other remote sensing applications such as natural hazard mitigation, water resource management and agriculture monitoring. It cautioned that further budget cuts would cause severe program dislocations.

The report was favorably received in the Senate, where appropriators gave MTPE/EOS a significant boost by recommending a modest $61 million budget cut. The Senate committee wrote that the review had “reaffirmed the program goal and overall approach of providing a scientific understanding of the Earth as an integrated system.”

During the ensuing months, Congress engaged in a high-stakes battle over the budget, which included several government shutdowns. Walker tried to leverage this fight to gain support for his proposed cuts, but Senate opposition cost him even the support of Rep. Jerry Lewis (R-Calif.), who chaired the key House appropriations subcommittee and argued that these efforts were pointless because they were opposed in the upper chamber.

In the end, the final omnibus bill only cut the MTPE/EOS budget by $91 million and accepted NASA’s long-term plan for the initiative. Walker continued his efforts to eliminate the program for another year, but he failed. In 1997, he retired. Scientists had won a significant, if little reported, victory in the climate wars. Three years later, the first EOS satellite, named Terra, was successfully launched into orbit and began returning data to terrestrial researchers.

During the past two decades, NASA has successfully battled to maintain funding for EOS, sustaining a robust earth science research program. The space agency has launched 26 Earth-observing satellites, and more are planned for the future. Combined with in situ observations, scientists are using the data from these orbiting platforms every day to increase their collective knowledge of how our planet’s climate system works. The increased scientific certainty that has characterized the climate change debate in recent years is partially a result of the failure to kill MTPE/EOS in the crib.

While moderate Republicans were once a key force in saving MTPE/EOS, their numbers have dwindled over the past two-plus decades. Today, the Republican Party is dominated by conservative voices like those found in the House in 1995, and climate denialism has become central to Republican voters’ identities. As a result, while the Senate has a new bipartisan climate caucus, the number of moderates in the chamber has probably fallen too far to rely on Republican support to shepherd through Congress the sort of comprehensive climate legislation required by the magnitude of the problem.

What was once an intraparty battle between the likes of Bush and Senate moderates, who believed in environmental stewardship, and conservatives allied with the fossil-fuel industry, is today a battle between a staunchly anti-science Republican Party and Democrats who see climate change as an urgent priority.

That means the outcome of legislation addressing climate change is likely to hinge on the outcome of the 2020 elections: Only Democratic victories can restore the United States to the Paris accords and make further action possible.