Disinformation and calls to violence clearly helped fuel the recent assault on our nation’s capitol, and an ongoing flood of disinformation now continues to subvert the reality of what happened. Yet as we assign blame for that destructive stream of disinformation, a deeply complicit stakeholder has largely been ignored — advertisers.

Obviously, President Trump has received a substantial amount of the blame for inciting the D.C. insurrection, as have select members of Congresssocial media platforms, and partisan “news” networks. Cable and satellite systems that distribute these networks have also been called into question.

Advertisers, however, help keep this dangerous current of disinformation flowing. Advertisers provide the lifeblood for a media ecosystem that has become a well-oiled lie machine. Advertisers today have an unprecedented array of options for where and how to allocate their advertising dollars, yet many continue to support outlets that are systematic disseminators of falsity. This needs to stop.

The journalism watchdog organization NewsGuard released a report earlier this month showing that over 1,600 brands placed online ads on sites that NewsGuard has documented as disinformation purveyors. Procter & Gamble, Disney and Walmart are some of the most high-profile companies whose ad dollars have helped to keep these sites afloat. Even nonprofit organizations such as the American Cancer Society, the AARP and Planned Parenthood have run ads on these sites.

The problem is worsened online by “programmatic media buying,” which is the automated process of placing ads on individual sites. Media buyers engage with intermediaries known as ad networks, which algorithmically place ads across the multitude of sites in their networks, leaving advertisers unaware of where these ads actually end up. In the wake of the 2016 election, some ad networks dropped known disinformation purveyors, but as the NewsGuard report shows, there clearly has not been enough progress on that front.

However, companies that advertise on television and radio programs that peddle disinformation cannot claim ignorance. Consider, for instance, Fox News’ “Sean Hannity Show,” a frequent offender on the disinformation front. Our own monitoring of a recent broadcast of the show found that it was being supported by well-known brands such as HBO, NBC, Lincoln Motors, La-Z-Boy, NutriSystem and SlimFast.

These advertisers need to take their share of responsibility for the health of our democracy and stop supporting outlets that are well-documented disinformation purveyors. As the events of January 6th have shown, the stakes are now too high and the substance and tenor of the disinformation have become far too dangerous for advertisers to be complicit, whether through apathy or ignorance.

Importantly, advertisers also should hold left-leaning networks to exactly the same standards as those on the right, since many programs on left-leaning networks also perform poorly (though not as poorly) in terms of basic adherence to the facts.

The groundwork for more wide-ranging action has been laid. The recently created Global Alliance for Responsible Media, a consortium of advertisers, is working to assure that brands don’t help monetize harmful content. The Inflammatory News Index, an analytics tool, can help advertisers avoid placing ads alongside news that contains misinformation, disinformation or inflammatory political rhetoric. NewsGuard offers a similar tool called BrandGuard. Last week it was revealed that after the election, shareholders in Home Depot and Omnicon pressured these companies to investigate whether they supported disinformation sources. Clearly, however, the continued economic viability of so many disinformation peddlers, and the events of January 6th, indicate that much more needs to be done.

Some might decry as censorship the idea that advertisers should base ad spending on an outlet’s’ record of demonstrable falsehood. Nothing could be further from the truth. Rather, this is exactly how the celebrated “marketplace of ideas” is supposed to work. In the marketplace of ideas, good ideas should compete with — and overcome — bad ideas. Truth is supposed to do battle with — and eclipse — falsity.

Advertisers are not just participants in the economic marketplace, where traditional goods and services are bought and sold. They are also key participants in the marketplace of ideas, where political ideas and viewpoints compete for attention and acceptance. Corporations have speech rights, and their allocation of advertising dollars is an established extension of speech rights in the U.S.

The problem is that these two marketplaces intersect. Advertisers’ demand for persuadable audiences in the economic marketplace leads them to become indiscriminate consumers in the idea marketplace. Companies and organizations support outlets for the audiences they deliver without adequately considering the kind of content they disseminate.

This imbalance in priorities has contributed to what can perhaps best be described as a market failure in the marketplace of ideas. The foundation of a well-functioning democracy is an informed citizenry. For that reason, if this market failure continues, our democracy may suffer irreparable damage.

Advertisers have tremendous power to push our media ecosystem back in the right direction, to help correct this market failure in the marketplace of ideas by avoiding outlets that peddle lies. Now is the time for them to use it.

Philip M. Napoli is the James R. Shepley Professor of Public Policy in the Sanford School of Public Policy at Duke University, and author of Social Media and the Public Interest: Media Regulation in the Disinformation Age.

Asa Royal is an Associate in Research at the DeWitt Wallace Center for Media & Democracy at Duke University.