A pediatrician holds a dose of the measles-mumps-rubella (MMR) vaccine at his practice in Northridge, Calif. (AP Photo/Damian Dovarganes)

There were a lot of half-truths and out-right falsehoods peddled at CNN’s Republican debate Wednesday night, but perhaps the most damaging among them was the assertion by Donald Trump that childhood vaccinations cause autism, and others’ skepticism about the safety of the vaccine schedule set out by the American Academy of Pediatrics. It was particularly galling watching two physicians who are president candidates, Ben Carson and Rand Paul, pander when they clearly know better.

Those who saw the vaccine exchange during the debate will rightly castigate the Republican field for their refusal to stand up for medical science consensus. But CNN’s role in raising the issue in the first place should not be overlooked.

If CNN, and other media, continues on the course of unprecedented politicization of vaccine safety by treating it as a campaign issue, the societal consensus on the safety and efficacy of vaccines may be eroded at tremendous cost. Here’s why.

We are fortunate to have a rather broad societal consensus on the efficacy and safety of childhood vaccinations. For all the attention that the anti-vaxxer movement has generated, vaccination rates for measles, mumps and rubella (MMR) remain above the 90 percent target in almost all states. Increasing resistance to vaccinations, while deeply troubling, has remained largely localized.

Further, as Kahan and others have noted, there are no striking partisan or ideological differences in vaccine attitudes. Notwithstanding the quackery on stage at the GOP debate on Wednesday, Republican voters are just as likely to believe in vaccine safety as Democrats, at least for now. That may change if party elites become polarized on the issue, and if this is communicated to the mass public through the national press.

We fear that it might happen because something similar transpired with attitudes about global warming. In a paper we recently presented at the annual meeting of the American Political Science Association, we looked at the role mainstream media plays in promoting pseudo-scientific attitudes on several issues, such as global warming and childhood vaccinations. We fear that the story of global warming polarization should serve as a cautionary tale of how the media and the political establishment choose to proceed on vaccinations.

So far the coverage of vaccinations has been reasonable, despite what we might intuitively infer from the rise of the anti-vaxxer movement. We know this because we gathered coverage of childhood vaccinations in the New York Times, The Washington Post, and USA Today, and constructed a keyword-based dictionary to capture cues from parties and party leaders, as well as experts using Lexicoder for automated content analysis.

The figure below shows that coverage of vaccines has increased since the bogus Wakefield study purportedly linked vaccines to autism. Salience has increased modestly, but politicization hasn’t. As the right panel shows, references to experts dominate coverage, and party cues have fallen to below 10 percent.

Do note that until recently, party elites were in consensus on vaccines. While some cues were present in the press, these did not have the potential to polarize the public.

We fear that if party elites continue to polarize, the cues present in the press could begin to undermine the societal consensus on childhood vaccinations. Why are we reasonably sure this is the case? Because we have seen this movie before, with global warming.

Climate scientists and others in the academic community have been at a loss as to why it has been so difficult to mobilize a societal consensus to take serious action in tackling global warming. The issue is polarized, with Republicans, particularly the most educated, being steadfastly against the scientific consensus. This fact has helped maintain a narrative in the press that Republicans and conservatives are inherently anti-science.

The narrative, however plausible on its face, ignores the fact conservative leaders in other countries got on board to deal with global warming (Margaret Thatcher and David Cameron, for example), and more importantly, over-time dynamics in the United States. Republican elites moved into a much more entrenched stance against dealing with global warming, and Republican voters became more skeptical over time. We gathered polls on global warming attitudes going back to 1992 from the Roper database, and constructed a climate skepticism “mood” measure using James Stimson’s WCalc software. The results are shown below in the furthest left panel.

Widespread polarization on global warming was not inevitable. As the left panel of the figure above demonstrates, skepticism has gradually crept upwards since 1992, almost certainly concentrated among Republican voters (for more details, please see our conference paper).

Two periods in particular are worthy of note: a steady increase in skepticism between 1992 and 2000, and a steep increase after 2006. Why did this occur? In all likelihood, an important contributor was a steep increase in the politicization of coverage, and the issue’s increased salience over time. Republican voters were persuaded by Republican and Democratic elites whose stances on the issue were increasingly available in coverage.

As we show in the center panel above, media attention on global warming skyrocketed after 2006, while the panel on the right shows coverage has gotten increasingly politicized. Parties and party leaders were hardly mentioned in the 1980s — now they are featured in over half of stories on global warming.

The period of increasing climate skepticism between 1992 and 2000 shown above corresponds with a period of relentless increases in the politicization of coverage, and increasing skepticism after 2007 may well be linked to a massive increase in coverage that made politicized coverage ever more available to Republican voters.

We believe the media played a critical role in polarizing the American public on climate change with potentially disastrous consequences in the future. Interest groups pressured Republican elites to reject action on climate change, and elite cues filtered through the press to erode Republican support of climate science.

We fear we may begin to witness a similar dynamic on vaccines. Republican elites are increasingly voicing skepticism of the medical science consensus. The media sees this as fitting a pre-established narrative that Republicans are hostile to science, and thus CNN asked the GOP field a question about vaccines in front of a record breaking national audience of 23 million people.

It would not be surprising if Democratic elites leap at this opportunity to solidify their own science-based credentials and make it a campaign issue, particularly if someone like Donald Trump wins the Republican nomination. These cues are then communicated to the public through the press, and we may be off to the polarization races.

Even a slight erosion in public support for vaccines may cause tremendous damage. We need at least 90 percent of parents to vaccinate their kids, not 60 percent or even 80. We should definitely be critical about Republican leaders pandering to vaccine truther-ism, but we should be equally critical of CNN for making this an issue in the first place.

If we value our societal consensus on vaccines, we must recognize that it’s potentially fragile, and that the best way to maintain it is to keep the issue out of the Republican primaries and out of the 2016 presidential election.

Eric Merkley and Dominik Stecula are PhD students in political science at the University of British Columbia.