Reply #21: Again, the issue is whether the US can apply the laws of war in a conflict with Justin Bieber.

[BzaDem]

Since Justin Bieber is present in the US, US law would govern, and he would have the due process rights afforded to anyone present in the US (citizen or non-citizen).

If there was a mythical Justin Bieber present in another country that commanded a terrorist organization that declared war on the United States, was actively planning terrorist attacks on the United States, etc, then the US could apply the laws of war to fight the terrorist organization and its members. (It might need domestic law authorization from Congress, such as the Authorization to use Military Force of 2001 or something similar.) This is not to say it necessarily would; if the organization was based in say France, the US would likely work with French police (rather than invade France's sovereignty), presuming we had confidence that the French wouldn't help them escape if we shared intelligence with them.