Americans have a much better chance of being killed by lighting than by a terrorist attack on US soil.
The FBI points out that it has caught tons of terrorists in the process of plotting attacks. In reality, however, most of these people have been caught in undercover operations.
In these undercover operations, individuals without ties to major terrorist organizations had vague ideas about harming the US, but no access to weapons or concrete plans.
Undercover agents set up deals to get them weapons, and than arrest them and tout it as a foiled plot.
Seems like our defense budget is way out of proportion with the threats we face.
In my opinion, terrorism is a law enforcement problem--not an existential threat--and not a military issue.