The Constitution does make the president “commander in chief,” a title President Bush often invokes. But it does not have the sweeping meaning he suggests. The framers took it from the British military, which used it to denote the highest-ranking official in a theater of battle. Alexander Hamilton emphasized in Federalist No. 69 that the president would be “nothing more” than “first general and admiral,” responsible for “command and direction” of military forces.
The founders would have been astonished by President Bush’s assertion that Congress should simply write him blank checks for war. They gave Congress the power of the purse so it would have leverage to force the president to execute their laws properly. Madison described Congress’s control over spending as “the most complete and effectual weapon with which any constitution can arm the immediate representatives of the people, for obtaining a redress of every grievance, and for carrying into effect every just and salutary measure.”
Read it all. Congress is certainly well within its intended authority to use the power of the purse to affect the President's foriegn and military policy. That's the whole point.