> ostensibly only after terrorists

Only wittingly.

"First they came for the Socialists, and I did not speak out— Because I was not a Socialist.

Then they came for the Trade Unionists, and I did not speak out— Because I was not a Trade Unionist.

Then they came for the Jews, and I did not speak out— Because I was not a Jew.

Then they came for me—and there was no one left to speak for me."

And, as ridiculous and slipshod as the whole thing is, the NSA is at least subject to some degree of oversight and regulation.

I don't know where you got this idea. The NSA is known for being close to useless in terrorism matters and champion of industrial espionage and spying on political leaders.