The recent truck bombing of the U.S. combat outpost in the village of Sadah in Diyala province—a bombing that killed nine soldiers from the 82nd Airborne Division and injured twenty others—reveals one of the trade-offs of the new strategy that General David Petraeus is adopting. By pushing more troops off their giant Forward Operating Bases (FOB’s), Petraeus is, at least in the short term, increasing their vulnerability. The smaller the outpost, the harder it is to defend.

Giant FOB’s like the Camp Victory/Camp Liberty complex near Baghdad Airport are almost invulnerable to ground attack. They are heavily barricaded and guarded; any VBIED (vehicle-borne improvised explosive device) going off at an entrance would do scant damage because the bulk of American personnel are miles away. The only real danger is occasional mortar or rocket fire—what the military calls “IDF,” indirect fire—which occasionally hurts someone but more often lands harmlessly. (There were several such attacks while I was at Camp Victory recently.)

By contrast, the Sadah outpost was set up in a school, with the perimeter relatively close to the building that housed American troops. According to Sudarsan Raghavan and Thomas E. Ricks of the Washington Post, one suicide bomber was able to ram his truck into a checkpoint, blasting a hole. Another truck filled with explosives passed through this hole, reaching a concrete wall only 90 feet from the building housing our troops. This building itself was not penetrated by either truck, but the blast waves were close enough to do serious structural damage, causing death and injury to those nearby and inside. Some soldiers were even buried in the rubble.

This is a tragedy. And, unfortunately, we can expect more of the same. Insurgents will continue testing our new Combat Outposts (COP’s) and Joint Security Stations (JSS’s) with car bombs, mortars, and perhaps even infantry assaults until they are convinced that these attacks will not deter us from expanding our presence. (Or until we decide to pull back.)

But the strategy of concentrating U.S. troops in giant bases, though superficially alluring, carries its own heavy risks. The biggest risk of all is that the troops won’t be able to accomplish the job they were sent to do. You can’t wage counterinsurgency from a long distance. You have to live among the people you’re defending. When U.S. soldiers commute to work in Humvees, not only do they find themselves unable to control their AOR’s (Areas of Responsibility), they also find themselves vulnerable to roadside bombs. By getting to know their neighborhoods—which, in most cases, requires foot patrols—troops can gather the intelligence necessary to round up insurgents and establish security for the population.

Over time this strategy will decrease risks not only for Iraqis but also for American troops. But the short-term costs will be real, as the Sadah bombing showed.