This is a poor justification, Bushie. Here's why: http://www4.law.cornell.edu/uscode/html/uscode50/usc_sec_50_00001805----000-.html So you can wiretap and then get retroactive warrants afterwards in case of an emergency. Wiretapping sans warrants is nothing but a blatant abuse of power.
Sadly, getting illegal wiretaps may weaken the war on terror as any indictments thereby obtained may well be thrown out. Some of the other terror related criminal prosectuions brought by the Bushies have been thrown out due to tortured confessions or the unwillingness to bring witnesses from secret prisons to testify.