It's not about the body count. It's about instilling fear and confidence in the government.

The US government's approach is pretty obvious is to attempt to prevent attacks through various means (reducing risks at airpoint checkpoints, keeping tabs on ammonium nitrate sales, etc), pursing investigations of people deemed vulnerable to terrorist manipulation, and blunting the impact of anything that does happen. When you watch the public coverage when something happens, there's a few common narratives, and they are always focused on portraying the offenders as loners who "aren't taking orders" from anyone.