Crooks and Liars points out that not only was the detention of Al-Marri violating the Consitution, it specifically violated the Patriot Act.

In sum, Congress has carefully prescribed the process by which it wishes to permit detention of “terrorist aliens” within the United States, and has expressly prohibited the indefinite detention the President seeks here. The Government’s argument that the President may indefinitely detain al-Marri is thus contrary to Congress’s expressed will.

But who cares about the law?! They’re terrorists!