Here's an attempt to find a correlation between coalition troops levels and Iraqi violence. It's hard to find any. But that could merely mean that we never saw anything like the massive force that would have a real impact. I fear merely adding 20,000 troops will be insufficient - within the parameters already tried and already failed. Adding 100,000 would be different. But we don't have 100,000 easily transferred. Given limited resources, what should we do? Bruce Rolston argues for adding 8,000 more troops to Afghanistan instead. His argument is worth listening to.