Many British people pride themselves on their equanimity and tolerance. Their motto could be "Live and let live." But Monday's horrendous suicide-bomb attack at Manchester Arena, which killed twenty-two people, many of them young girls who had been attending an Ariana Grande concert, has tested this resolve. The bomber, Salman Abedi, a twenty-two year old Mancunian whose parents are Libyan, appears to have been a homegrown militant jihadi, one of a significant number of young Britons who have become radicalized in recent years.

In the immediate aftermath of the atrocity, some British commentators demanded drastic actions. "22 dead—number rising," Katie Hopkins, a columnist for the Daily Mail, wrote on Twitter, on Tuesday morning. "Do not be part of the problem. We need a final solution." (After objections from Jewish groups and others, Hopkins deleted the tweet and sent a new message, which said, "We need a true solution.") Allison Pearson, a columnist for the Daily Telegraph, tweeted, "We need a State of Emergency as France has. We need internment of thousands of terror suspects now to protect our children." The singer Morrissey, who grew up in Manchester, berated Theresa May, the Prime Minister, and other politicians.

These opinions didn't necessarily reflect a general consensus: indeed, their progenitors were responding to what they viewed as soggy and complacent responses from others. In central Manchester on Tuesday night, thousands of people, including senior politicians from all the major parties, attended a peace vigil at which the city's Lord Mayor, Eddy Newman, said, "We will defy the terrorists by working together to create cohesive, diverse communities that are stronger together. We are the many, they are the few." (Ed Caesar wrote a piece about the vigil for this Web site.) During a visit to Manchester on Tuesday, May saluted the city's “unbreakable spirit,” and wrote in a condolence book, "Terrorism never wins, our country and our way of life will prevail."

Later on Tuesday, May announced that the government was raising its official terror-threat level from "severe" to "critical," indicating that the police couldn't rule out the possibility that Abedi had accomplices who might be preparing another attack. May also said that the government would deploy as many as five thousand troops to guard strategic sites, such as Buckingham Palace and Downing Street.

On Wednesday, those soldiers started moving into place, and the head of the Greater Manchester Police said that the authorities were investigating the possibility of “a network” linked to the bomber. The New York Times published pictures of bomb components discovered at the scene of the explosion, and reported that they came from an "improvised device made with forethought and care," in which "shrapnel was carefully and evenly packed."

May described the elevated threat level and the rolling out of troops as "a proportionate and sensible response" to the bombing. But, in a country where most police officers are still unarmed and uniformed soldiers almost always remain confined to their barracks, the actions she approved marked a break with tradition—one that unnerved some liberal observers. "Troops are being deployed in the middle of a general election campaign," Jonathan Friedland wrote in the Guardian, on Wednesday. "That is new and unsettling terrain for British democracy."

I grew up in Leeds, which is about forty-five miles from Manchester, and my youngest brother, Peter, still lives there. He told me that, since the attack, the predominant feeling in the area is still one of shock and horror. The thousands of young women and girls who attended Monday’s concert had travelled from all over the country for the chance to see Ariana Grande, and the heartbreaking stories of both the victims and survivors are just now emerging in the media. "Attacking the Houses of Parliament, that was one thing," Peter said, referring to the incident in March, when a fifty-two-year-old Muslim convert drove his car into pedestrians on Westminster Bridge, causing the deaths of four people, then fatally stabbed a police officer. "But blowing up little girls . . ."

Unfortunately, Manchester isn't the only place in England to have a problem with homegrown jihadis, and the problem isn't a new one. Khalid Masood, who carried out the attack on Westminster, was born in Kent and had been living in Birmingham. Three of the four young men who carried out the 2005 bombings on the London Underground came from Leeds. (The house that they used as a bomb factory is about a mile from where my brothers and I once lived.) That atrocity took the lives of fifty-two people, but, when it wasn't immediately followed by other attacks of the same scale, Britons felt reassured that the threat could be contained.

Even before Monday’s bombing, though, that confidence had been shaken. The British government has estimated that more than eight hundred people from the U.K. have gone to fight with ISIS in Syria, and many of them are believed to have returned home. Before Monday, the police's anti-terrorism units had reportedly foiled about a dozen suspected conspiracies this year. The authorities knew that they couldn't hope to prevent absolutely every attack, but they had focussed on what they saw as the main threats, and had beefed up security where possible.

The soldiers deployed in response to the Manchester bombing marked an escalation of this approach, rather than a shift to more draconian measures, such as making mass arrests and detaining suspects for long periods without trial. Britain tried that tactic in Northern Ireland during the nineteen-seventies, and it just created more recruits for the I.R.A.

So far, practically all the politicians at Westminster, and most Fleet Street newspapers, have backed a measured approach. "It is impossible to intercept every threat," the upmarket Financial Times said, in an editorial on Wednesday. "Citizens must accept that we live in an insecure world." The mass-market Sun, which sees itself as the voice of the jingoistic working man, didn’t display that sort of sang-froid. But it did reject the most extreme options. "Some want all Isis suspects or sympathisers we know about ‘interned,’ locked up without trial," it said. "The Sun cannot justify that. It throws fuel on the fire."