Genuine Risk,
Here is the link to the Military Commissions Act of 2006. S3930.
On page four you'll might note section C, "Determination of Unlawful Enemy Combatant Status", and who makes the determination.
http://thomas.loc.gov/cgi-bin/query/z?c109:S.+3930:
btw, I've read the Constitution of The United States many times. The powers of each of the three branches of government are clearly stated.
The Legislative branch makes laws. The Executive branch executes (enforces) them.
I hope that those that doubt what you've said take the time to read the Military Commissions Act of 2006.