>
it happened once when Anwar al-Awlaki was killed in a drone strike.There have been three US citizens[2] killed by two separate drone strikes. Anwar al-Awlaki is one; in that same strike also killed was Samir Khan — the very Wikipedia article you linked to mentions this. In a separate strike[1], Abdulrahman Anwar al-Awlaki (the son of Anwar), a 16 year old with "no connection to terrorism", was killed.
> You say this like it's an everyday occurrence
Even that it isn't an everyday occurrence, how does that justify taking the life of an American citizen without providing due process to that citizen?
> procedures to protect against accidental or inadvertant surveillance of citizens
This is not even remotely true; the Wikipedia article on the NSA states that the NSA "[relies] on a secret interpretation of the Patriot Act whereby the entirety of US communications may be considered 'relevant' to a terrorism investigation if it is expected that even a tiny minority may relate to terrorism"; the 120 million Verizon subscribers whose data was collected were protected against "accidental or inadvertant surveillance"?
Programs such as MUSCULAR[3] gathered data secretly on American companies' data-center links.
But let's consider that perhaps you don't believe "merely" spying on someone to be a violation of the constitution; let's say that the collected information needs to be actually used against a citizen:
> In August 2013 it was revealed that a 2005 IRS training document showed that NSA intelligence intercepts and wiretaps, both foreign and domestic, were being supplied to the Drug Enforcement Administration (DEA) and Internal Revenue Service (IRS) and were illegally used to launch criminal investigations of US citizens. Law enforcement agents were directed to conceal how the investigations began and recreate an apparently legal investigative trail by re-obtaining the same evidence by other means.
(emphasis mine)
[1]: https://en.wikipedia.org/wiki/Abdulrahman_al-Awlaki
[2]: https://www.aclu.org/cases/al-aulaqi-v-panetta-constitutiona...
[3]: https://en.wikipedia.org/wiki/MUSCULAR_(surveillance_program...