We already know that Fox News exerts an outsized influence on executive decision-making in the US. Donald Trump’s out-of-hours tweets are frequently responses to the latest coverage on the right-wing news channel, and while the president is known rarely to read his briefings, he regularly regurgitates Fox stories.

Earlier this year, the journalist Luke O’Neil gathered stories from a dozen people who believed that their relationships had suffered because close friends or family members had become obsessed with Fox News. The piece attracted hundreds of responses from readers who had experienced the same. Their stories followed a similar arc, O’Neil wrote in New York Magazine: “A loved one seemed to have changed over time. Maybe that person was already somewhat conservative to start. Maybe they were apolitical. But at one point or another, they sat down in front of Fox News, found some kind of deep, addictive comfort in the anger and paranoia, and became a different person.”

The “hardest thing” O’Neil learned was that: “Fox didn’t necessarily change anyone’s mind, so much as it seems to have supercharged and weaponised a politics that was otherwise easy for white Americans to overlook in their loved ones.”

A recent study suggests that Fox News has another big, and more insidious, effect on American political life. Research by Elliott Ash (an assistant professor of law, economics and data science at ETH Zurich) and Michael Poyker (a postdoctoral researcher at New York’s Columbia University) suggests that greater exposure to Fox News causes American judges to impose harsher criminal sentences – particularly against black defendants, and in drugs cases. They estimate that increasing Fox’s viewership share by 1 per cent leads to a four-month increase in the average prison sentence.

The link between Fox and harsher sentencing was only observed among elected judges, not those who are appointed. This suggests that the problem isn’t that the judges have internalised cable news biases, but that they are responding to a Fox-watching electorate with a punitive view of justice.

So how do we know that Fox is to blame? Is this not a case of right-wing voters preferring tough-on-crime judges? Ash and Poyker were able to rule this out because they didn’t measure Fox viewership directly. Instead, they looked at the channel setting for Fox News, CNN and MSNBC in each county studied.

Cable channel numbers were mostly set in the nineties, and vary randomly between cable providers and by county. Most people are lazy, and if they want to watch the news they turn on their TV to channel one and then keep clicking until they hit a news programme. If they reach Fox before they reach CNN, they tend to watch Fox, regardless of their political leanings. This means that areas in which Fox has a lower channel number tend to have more Fox viewers, and social scientists can isolate the Fox News effect from other right-wing cultural and political forces. Another study has shown that parts of the country in which Fox was randomly assigned a lower channel number are more likely to vote Republican – suggesting that the news network influences voter preferences.

Ash and Poyker analysed the language used in crime stories by Fox, CNN and MSNBC and found that while CNN is more focused on organised crime, frequently using terms such as “mobster” and “terrorism-related”, Fox often presents crime as a racial issue, referring to “black-on-white” crime and, less often, “white-on-black” crime. It commonly uses terms such as “perps” or “priors” that dehumanise defendants. They believe this kind of coverage might prompt Fox viewers to vote for harsher judges, and elected judges to adjust their sentencing accordingly.

The US locks up more of its citizens than any other country. There are 2.3 million people incarcerated in American jails, and a disproportionate number of them are people of colour. There is growing political agreement that this needs to change, but papers such as this reveal just how many complex factors are driving mass incarceration. “The answer to this paper isn’t that we should ban Fox News, or introduce regulations to restrict the media,” Ash told me on the phone. “But I do think that it points the way towards reducing political influences on the judiciary.”

He believes it offers a strong argument against electing judges. Most people, after all, expect judges to apply the law without bias, and would consider it unfair that someone should spend longer in prison because a judge feels beholden to a Fox-watching electorate.

But research into the hidden ways in which media coverage influences public life and policymaking also underlines the responsibility of journalists to uphold standards of accuracy, impartiality, fairness and scepticism. While restricting press freedom never serves the public interest, if we are to move beyond this period of hyper-partisanship and “post-truth politics” many news organisations could begin by scrutinising themselves.