AB says US defenses against roadside bombs are improving: sophisticated devices that jam the electronic signals used to set off roadside bombs are employed now in US humvees but they're not effective against wired bombs. The US is also using new vehicles which has armor which has led to some reductions in US casualties. (What about soldiers being in the neighborhoods of Baghdad and getting Iraqis to trust them better?) The US military maintains that part of the troop surge are these kinds of new tactics, like dispersing US troops more widely. Troops are now based permanently out on their own in communities. The US military maintains that has made a difference in building ties with local communities. (Does that also mean the US troops are more vulnerable?) some things have worked to counteract that vulnerability: the larger number of US troops, another factor is experience among US troops. Other things going on beyond the Americans' control: the largest Shiite militia is holding to their ceasefire, large numbers of Sunni Iraqis have turned around and are cooperating in surprising ways. The calculation that these militias make is beyond the reach of the US military and the US military is wondering how long these developments will continue. (What does the number of 4,000 Americans killed in Iraq mean for troop morale?) If you look back at the number of Americans who have died, when and how they've died, one important factor is that the majority of these deaths came in 2004 when the US was engaged in fierce combat. Then the numbers go down and fluctuate wildly, until 2007 when the US tried to take down the entrenched insurgents. In terms of morale, it feels like the US has a stronger footing in Iraq than in the past, but they're also focused now on a post-surge Iraq and making that successful, and nobody in the military has got answers on that question yet.