Candles surround a tribute to Labour MP Jo Cox before a vigil in her memory in George Square in Glasgow, Scotland. (Jeff J Mitchell/Getty Images)

Every era has its own form of mental illness; madness takes forms that suit the times. Hysteria, the disease that Freud spent so much time trying to understand, is no longer recognized or diagnosed. Anorexia, once relatively rare, is now far more common.

Every era has its own political rhetoric, too, and this also affects the human brain. In the past week, two men have committed murder in highly charged circumstances. Were their actions the result of personality disorders, or were they political? What if the answer is “both”?

In Orlando, Omar Mateen killed 49 people in a gay nightclub. Before doing so, he wrote on his Facebook page that “The real muslims will never accept the filthy ways of the west” and “You kill innocent women and children by doing us airstrikes..now taste the Islamic state vengeance.” He made an open threat: “In the next few days you will see attacks from the Islamic state in the usa.” Yet there is still no evidence that he had any real connection to the Islamic State. Although his language was radical enough to inspire an FBI investigation, no direct links have been found. At the same time, Mateen abused his ex-wife; a local imam has described him as reclusive. A former colleague has said, “He talked about killing people all the time,” hardly a sign of mental balance.

Was Mateen a “terrorist”? A “lone gunman”? Can he be accurately linked to the Islamic State if he had never met any of its members?

In the Yorkshire town of Birstall, Tommy Mair has been detained in Thursday’s killing of Jo Cox, a Labour member of Parliament who was actively campaigning for Britain to remain within the European Union, and actively campaigning on behalf of Syrian refugees, too. Two witnesses say that Mair, a reader of neo-Nazi and white supremacist books and websites, according to the Southern Poverty Law Center, shouted “Britain first” while stabbing Cox.

This crime was committed on the same day that the anti-European UK Independence Party launched a poster featuring a crowd of Syrian refugees and the slogan “Breaking Point,” following weeks of tabloid headlines about the danger that immigrants pose to the British health service, British schools, the British way of life. But Mair also has a history of mental-health problems for which he had been actively treated; he seems to have had no job or friends. Was he inspired by the unusually angry referendum campaign? Can a man with mental-health issues be legitimately said to have been inspired by media rhetoric?

Just as Americans have fought over the correct description of Mateen, the British do not agree about Mair. On Friday morning, the Sun, an anti-European tabloid, said Cox had been murdered by a “crazed loner.” The Guardian, like other pro-European newspapers, quoted Cox’s husband, who called on Britain to fight “the hatred that killed her.” The rest of the British press split their descriptions of him along ideological lines, too.

This dispute will not be resolved, because it can’t be. It is not possible to separate the strands of emotion, justification, madness, calculation, reason and fanaticism that can exist in a single human brain. But neither is it possible to separate the human brain from its environment.

And that environment is toxic: Though more information will surely emerge, we already know enough to understand that the Orlando massacre and the murder of Cox were political crimes, and that they cannot be explained without reference to political rhetoric. Mateen used violent political language to describe what he was doing. He appears to have been inspired by a jihadist Islamist political movement, even if he personally knew none of its members. Mair is not suspected of killing a random person at a random moment, either: This was the murder of a prominent politician at the height of an angry and emotional referendum campaign.

The hateful jihadism that spreads through the Internet and the airwaves; the vicious, nativist rhetoric that tells voters they will soon be swamped or broken, that they must fight to take their country back from an unnamed enemy — these are the ideas that shape the world we live in. And, yes, these are the ideas that will inspire the madmen and murderers of our era, too.

Read more from Anne Applebaum’s archive, follow her on Twitter or subscribe to her updates on Facebook.