Not an American, but I can totally understand the need of governments to spy on its citizens that it has EVIDENCE of being involved in behaviour or activities that threaten the nation.

For example - if it had evidence that certain citizens were involved in espionage of their country, and they were thus passing on serious information to actors or other states that were intent on using that information to harm the nation, I would most definitely want those citizens to be spied upon.

Such evidence could be: Engaging in, or communicating with, known extremist organisations or forums known to be frequented by such individuals.