We learned this week that in October 2001 famous Justice Department legal advisor (and now law prof) John Yoo authored a memo opining that the Fourth Amendment has "no application to domestic military operations." In context, "domestic military operations" apparently referred to surveillance programs conducted by the National Security Agency (the NSA is technically a military entity). The import of that view is that the federal government can, by using the talismanic "anti-terror investigation" label, wiretap conversations by Americans with no regard for the protections of the Fourth Amendment.
The Bush Administration has since rejected Yoo's interpretation, but may not have done so until sometime in 2003. I've never really bought into the liberal charges that (now former) key Justice Department officials like Yoo viewed the President as "above the law" in conducting the war on terror, but Yoo and company sure provided a lot of ammunition for that argument.