There is obviously no clear and agreed upon definition of the politically potent term terrorism. The phenomenon of people making violent attacks intended to serve some kind of political purpose has been going on pretty much since human societies became complex enough to have formal political institutions. However, in US political discourse since 9/11 use of the term seems to have some recurring themes. They are generally related to our perceptions of that attack and the fear that similar incidents could recur on a regular basis. Those elements include:
Organized and carried out by people who are not US citizens
Aimed at US civilians on US soil
Motivated by an anti-US ideoligical movement, most likely with an Islamic connection
The justifications that have been offered by government officials for the various activities of the NSA and CIA have focused on keeping Americans safe from threats that appear to fall within this framework.
There was one basic reason that the perpetrators of 9/11 were actually able to pull it off - sloppy airline security. If the procedures that were supposed to be in place had been closely adhered to, there is a very good chance that they would have been stopped at the gate. One of the first responses to the incident was establishing the TSA and that I believe is why we have not had another incident of similar airline violence. Airport security is annoying and inconvenient, but it definitely appears to be worth the investment.
As far as I can tell we really haven't had anymore terrorist attacks on American soil by non-US citizens. In the 12 years since 9/11 the first incident to come along that sort of qualifies is the Boston bombing earlier this year. We have had a number of reports of various plots, but nothing has actually happened. The Boston incident was carried out by two brothers who were US citizens at the time. What is of course ironic is that the older brother had been identified as someone with possible terrorist connections, but that information was not used to make any attempt to prevent the attacks.
In the meantime during those 12 years Americans have faced many other threats of violence and a number of them have lost their lives as a result. Three incidents that come quickly to mind are the mass shootings in Tucson, AZ, Aurora, CO and Newton, CN. The perpetrators of these incidents were white American men and are being labeled as mentally ill rather than ideologically motivated. There has been a strong public outcry for an effective government response to at least reduce the risk of such tragic occurrences. Our political system is paralyzed and unable to respond. These are of course just three very well known incidents. Americans die everyday because of gun accidents and deliberate gun violence.
We are being told that foreign terrorism poses such a horrible threat that we must expect to make compromises to strike a balance between our civil liberties and privacy on one hand and the need for national security on the other. This all strikes me as essentially disingenuous propaganda. The government is spending many billions on its ever expanding surveillance system. It is not doing that to protect Americans from something that poses a very minimal threat. The purposes lie elsewhere. We don't really know where the main focus of all this surveillance really is. Perhaps some of the information that is being revealed will shed some light on it.