They don't even need the pretext of finding out anything. These days they can pretty much get away with hauling you off and detaining you, denying you right to counsel and refusing to name the "charges" against you (because apparently telling you what you've done to be detained is a breach of security (which makes total sense, uh huh)). Even though the Supreme Court (a formerly equal branch of govt, but the Constitution is, as I mentioned, more of a guideline than actual rules) told the administration that this was illegal, they're still doing this.

We should all just shut up and trust them, because, God (and Thomas Jefferson, James Madison, Alexander Hamilton and Co.) knows, this country was founded on principles of keeping quiet and trusting the government. Especially a strong executive named George.