The president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation. As commander in chief, the president does have a duty to protect and defend the United States. In instances of self-defense, the president would be within his constitutional authority to act before advising Congress or seeking its consent.
The military has no constant form, just as water has no constant shape - adapt as you face the enemy, without letting them know beforehand what you are going to do.
The best way to fight evil is to do some good. Let me qualify that—the best way to fight evil at home is to do some good. The best way to fight them abroad is to unleash the military.