On the night of March 20, on the corner of Cambria and Rosehill Streets in Kensington, two city police stopped a car because one of its headlights was out.

At least that was the official reason. The neighborhood is known for drug trafficking and violence, and one suspects without much effort that the officers were intent on something more than improving motor vehicle safety. They were "fishing." As aggressive - the department prefers the adjective proactive - cops will, they were looking for trouble. Something interested them about the man behind the wheel.

The man was Rahman Jenkins, and, as it turns out, he was free on bail and awaiting trial on drug and weapons charges. According to the police account, Jenkins was armed with a 9mm Glock, and inside the car were 10 packets of cocaine and a box of ammunition.

Jenkins did not react well to being stopped, and, after a scuffle, was shot in the head and killed. There are mixed accounts, as there nearly always are, of how the shooting occurred, and whether it was warranted. He was the fifth man shot and killed by police this year, and there have been the usual (and appropriate) calls for investigation.

Beyond the particulars, this incident has larger implications now that Michael Nutter is well on his way to becoming the next mayor of Philadelphia. More than any other candidate, Nutter has rightly voiced the urgency of reducing the city's escalating gun violence.

The most controversial tactic he advocates, which has been much discussed, is called "stop-and-frisk," and would encourage the police to do more of what these two officers in Kensington were doing when they stopped Jenkins. Most of the discussion has concerned its potential for harassing innocent people. The tactic pushes at a sore point in the relationship between citizens and their police force, a place were civil liberties and the need to protect the public inevitably come into conflict.

One cop I know told me that this is exactly the kind of work he already does. He uses his training, knowledge and experience to initiate pedestrian and car stops that have a relatively high probability of leading to an arrest, preferably (as he put it) for a felony. The best officers snoop around looking for trouble, he said, and they find it.

And trouble, in a city loaded with handguns, all too often means violence. One of the certain consequences of encouraging "stop-and-frisk" is not just more complaints about police harassment, but more gun battles between suspects and police. It will almost certainly mean more shootings of police, and more shootings by police.

No one better appreciates this than cops, which is why only a fairly small number of officers practice "stop-and-frisk" now, mindful of the potential for both physical injury and public censure. Last year, city police shot and killed 20 people, the most since 1980, and they are on a pace to a higher number this year already. Officers like my friend the sergeant worry about the implications of that. "Stop-and-frisk" strains the relationship between citizens and police because plenty of innocent people who attract suspicion will be detained, and some cops are more polite and disciplined than others. Training can only go so far.

There can be anxious moments when a "citizen's" intentions and capability to inflict harm are unclear, and the use of force is not yet justified. In that instant, a cop notes the words and body language of someone who is on the verge of a violent attack, but has not yet committed himself to it. If the officer asks for a driver's license, and the suspect reaches for a large bulge in his pocket, is it a wallet, a cell phone, or a weapon? Does the officer wait to find out? Does he or she wait until a weapon is actually being pointed? Or does the officer shoot, while he or she still has the advantage? Whatever decision, it must be made in about three-tenths of a second.

Because most of those who are confronted (or shot) will be African American or Hispanic, police can foresee accusations of departmental racism, and wonder whether Nutter will be in their corner when the pressure mounts. Right now, the call for giving the police wider latitude has great appeal, but veteran cops know that the pendulum swings the other way. When it does, who pays the price?

I have not even mentioned the other practical consequences of more aggressive policing. It will mean more arrests, which means more trials and more prison sentences. Do we have the courts and cells to cope with such increases? If not, the usual results are lighter sentences and more probation, which could mean more convicted felons on the streets.

The answer to the current problem of violence is well beyond the scope of Nutter or any mayor, no matter how smart or well-intentioned. Lack of job opportunities, the breakdown of families, the drug culture, the condition of many city schools, and other pervasive urban ills have combined like some kind of witch's brew to produce an abandoned, violent and nihilistic youth subculture that cries out for some kind of national intervention. I don't know exactly what shape it should take, but it will have to be something more like one of FDR's New Deal programs than a change in local police tactics.

In the meantime, the best we can hope of soon-to-be Mayor Nutter, who has displayed both eloquence and outrage over this problem, is that he will use his passion and his platform at City Hall to help wake up Washington.

Mark Bowden is a former staff writer at The Inquirer and is now national correspondent for the Atlantic Monthly. Contact him at embolden@phillynews.com.