(e) AUTHORITIES.—Nothing in this section shall be construed to affect existing law or authorities relating to the detention of United States citizens, lawful resident aliens of the United States, or any other persons who are captured or arrested in the United States.
So, how does this give the president the supposed power to detain US citizens? (The oft quoted 'slippery' line about not requiring detention Americans is from the NEXT section, which is specifically about requiring detentions in some cases.