"I've heard this before and have searched the Constitution for this authority. I have written my congressmen and three Presidents to try and find out what clause granted the executive the authority to over ride law."
Article II Section 2 "The President shall be Commander in Chief of the Army and Navy of the United States and of the militia of the several states, when called into the Service of the United States.
FISA came after this, and FISA can not interfere with it or overrule it. Your suggestion that the President has "authority to over ride" law is backwards. The constitution comes first. The only way to override the constitution is by an amendment to the constitution. If our system of Government was the way you depict it, there would be no need for a constitution at all. We could simply make any law we wanted at any time to override the constitution.
If you read the preamble, it starts with "We the People of the United States", further it distinguishes between law enforcement "establish justice" and war "provide for the common defense". Criminal law and war were distinguished here and at other locations in the constitution. It is clear that the founders did not confuse the 2.