My experience of Blackhawk helicopters was restricted to Iraq -- until this morning, when I heard them flying low over the quiet, leafy Cambridge, Massachusetts, neighborhood where I’ve lived for most of my 42 years.

They landed in the parking lot of the Target store that I bike to with my kids, a couple of miles to the west of my home. Meanwhile, the same distance to the east, near Inman Square, the police are reportedly planning a controlled explosion a block from the S&S Delicatessen where we eat potato pancakes.

Bizarre and surreal as it seems, terrorism has come to Cambridge.

On the streets not far from Watertown, where police may have cornered the suspected bomber Dzhokar A. Tsarnaev, quiet reigns as most people comply with police requests to stay indoors. Sirens can be heard intermittently. The occasional pedestrian straggles down the block carrying a pizza. Yet a veneer of normalcy persists. Directly across the street from me, a construction crew got to work this morning before the warnings began -- and they stayed at it all morning, bringing a gut rehab one day’s work closer to completion.

Cambridge Shootout

If it weren’t for the news, it would be hard to believe that last night Cambridge was the site of multiple shootouts, a carjacking and a car chase -- or that an apparent standoff continues today. Indeed, the events covered the full breadth of this small city of 100,000 adjoining Boston. The marathon bombing suspects killed a Massachusetts Institute of Technology police officer in Kendall Square, at the far eastern end of town. They carjacked an SUV and then drove clear across town on scenic Memorial Drive, along the Charles River, eventually exchanging fire with police when they had passed the city’s western boundary -- the exchange in which Tamerlan Tsarnaev was killed.

About 9 p.m. yesterday, I was sitting at a dinner with Iraqi politicians, former George W. Bush administration officials and Iraq scholars at the Harvard Kennedy School, discussing Iraq’s severe political challenges. I heard unusually loud sirens as police vehicles crossed the Charles. I didn’t think much about it. My mind was in Baghdad, not Cambridge.

While the car chase and shootings were going on an hour or two later, I was sitting in a restaurant in Harvard Square, a couple of blocks from where they drove by -- and I heard nothing. I biked home, presumably in the middle of the events, and again noticed nothing out of the ordinary.

The comparison to Baghdad, where I worked for the transition authority after the 2003 U.S.-led invasion, is immediate for me -- and the bottom line is how different this seems from being in an actual war zone. Being asked to “shelter in place” makes you nervous for your kids and has you scouring the freezer, but it doesn’t feel like being locked down in the Green Zone in Baghdad.

Here’s why: When this tragedy is over, we will return to normal. By the end of the day, God and police willing, the remaining suspect will be dead or in custody. When that happens, we will return to the streets wiser, but not any less secure. We will be able to tell our children with total confidence that everything is now fine.

There is a crucial lesson here. A strong state cannot avoid terror. But it responds to terror with thousands of police, helicopters and the full weight of a security apparatus that has confidence in its ultimate success.

By contrast, in a weak or failing state, terror signals that more terror is coming -- it challenges the state’s very ability to function. The responders look weak, not strong. And the society looks fragile, not vital.

Two Extremes

Not every place is on the extremes of Cambridge’s stability or Baghdad’s disintegration. There is plenty of room in between. Last September I was in the parliament building in Tunis when protesters penetrated the perimeter of the U.S. Embassy in the Tunisian capital and clashed with police, leaving several protesters dead. There, the mood was a mixture of nervousness and calm -- life would probably return to normal, but things were also changing and therefore uncertain.

Here in Cambridge, the shock that it can happen here -- that innocent children and brave police officers can be killed in cold blood, apparently by our neighbors -- is mitigated by the knowledge that before too long, our state and society will bounce back. “Boston Strong” isn’t just a slogan. It is a description of what a healthy polity can do for itself in the face of crisis -- and what every state facing terror wishes it had.

(Noah Feldman, a law professor at Harvard University and the author of the forthcoming “Cool War: The Future of Global Competition,” is a Bloomberg View columnist. Follow him on Twitter. The opinions expressed are his own.)

To contact the writer of this article: Noah Feldman at noah_feldman@harvard.edu.

To contact the editor responsible for this article: Tobin Harshaw at tharshaw@bloomberg.net.