“Us versus them” has been Donald Trump’s theme since the beginning of his candidacy. But the more often he applies it, the more slippery and opportunistic those categories seem. Photograph by Damon Winter / The New York Times / Redux

"The Muslims have to work with us," Donald Trump said on Monday, in his speech responding to the slaughter of forty-nine people at Pulse, a gay night club in Orlando, by a twenty-nine-year-old Muslim-American security guard. He repeated, "They have to work with us. They know what's going on. They know that he was bad. They knew that the people in San Bernardino were bad. But you know what? They didn't turn them in. And you know what? We had death, and destruction."

“Us versus them” has been Trump’s theme since the beginning of his candidacy. But the more often he applies it, the more slippery and opportunistic those categories seem. A week ago, in his attack on Judge Gonzalo Curiel, Trump suggested that Hispanic-Americans might have divided loyalties. In Orlando, most of the dead were Hispanic-Americans, and so he pledged to protect “all Americans within our borders. Wherever they come from, wherever they were born, I don’t care.” Hispanics, formerly “them,” were all of a sudden “us.” Trump moved quickly toward a different “them,” Muslims, the people who “know what’s going on.” That same day, he suggested that Barack Obama’s own loyalties might be divided and that the President might have known about the attack in advance. (“He doesn’t get it, or he gets it better than anybody understands,” Trump said.) Echoing the candidate, Trump’s ally Roger Stone claimed that Huma Abedin, the vice-chair of Hillary Clinton’s campaign, could be a “Saudi spy” or “terrorist agent.”

In Trump’s speeches, lines of ethnic strife are always present but forever being rearranged—suddenly drawn, then erased, and then drawn again. The pattern shows an intellectual habit of Trump’s—ethnic essentialism, in which individuals are blurred out in favor of the groups to which they belong. Not Muslim-Americans, but "the Muslims." Not African-Americans, but "the blacks." (2011: "I've always had a great relationship with the blacks.") This talk is something of a relic of the New York of the nineteen-eighties, from which Trump himself emerged, suffused with ethnic competition and fear. It was Trump’s sensibility as a real-estate executive of that era, whose managers marked “C” for colored on rental applications. These views incline a business executive and those around him to acts of discrimination and bias. They have an additional effect in a politician trying to make sense of human events: they nudge him toward seeing the entire group as responsible, and blind him to the individual.

On Monday, the conflict Trump saw was between Muslims and everyone else. “If we want to protect the quality of life for all Americans—women and children, gay and straight, Jews and Christians and all people—then we need to tell the truth about radical Islam,” he said. But, as is almost always the case, the more we learned about the shooter’s life, the less to the point this sounded. At first, it was possible to see in Omar Mateen a recognizable character: a young, radicalized Muslim man who, on a 911 call just before his attack, pledged allegiance to ISIS. But, in the second news cycle, and then the third, complicating details emerged. Mateen’s father initially said that his son had been angered when he saw two men kissing in Miami, and that this might have inspired the attack, but it turned out that Mateen himself had been a regular at Pulse for years. Two other patrons told reporters that Mateen had recently messaged them via a gay dating app. Mateen's father has denied that his son was gay, and said, in apologizing for the attack, that “God himself will punish those involved in homosexuality.”

Mateen’s bigotry, in the descriptions collated in the news reports, belonged to a familiar American strain, sometimes animated by religion but sometimes not. A man named Daniel Gilroy, who worked with Mateen for about a year, said, "I complained multiple times that he was dangerous, that he didn't like blacks, women, lesbians, and Jews." The two men once saw an African-American man drive by them, Gilroy told the Los Angeles_ __Times, and Mateen said that he wished he could kill all black people, using a racial slur. "You meet bigots, but he was above and beyond," Gilroy said. "Just angry, sweating, angry at the world." Perhaps that anger and sweat had something to do with Islam, or with religiosity generally, but exactly how much is impossible to know. “The Muslims have to work with us,” Trump said. But that obscures the collective responsibility. Mateen was not “an Americanized guy,” as his ex-wife put it to the New York __Times_, but an American. His views were visible not just to his co-religionists but also to his co-workers. He was part of our society.

During the barnstorming, protectionist phase of Trump’s primary campaign, his tendency to talk about “the Chinese” or “the Mexicans” as though they were hive-minded actors seemed mostly to betray an allergy to nuance. But, as the general-election campaign has begun, the public scrutiny of Trump’s words has intensified. His ethnic essentialism, the dwelling on dual loyalties, has become not just a point of offense but an electoral problem. For months, some progressives have worried that a terrorist attack could tip the election to Trump, because he might be seen as an avatar of strength. That attack came on Sunday, and, after Trump’s scapegoating reply, those worries have eased. A Bloomberg poll released Tuesday showed Clinton leading her Republican rival by twelve percentage points; fifty-five per cent of likely voters polled swore that they would “never” vote for the casino mogul. It’s hard for Trump to be seen as a protector when it isn’t clear whom he would be willing to protect.