Limiting The President Of The United States Of America States United
The president is legally capable of initiating an offensive without an actual declaration of war. He must simply get congress to approve his act of war within ninety days or cease those efforts.
The idea is that the commander of our forces should be capable of responding to a serious threat immediately, rather than waiting around for councilmen to deliberate. A precaution I approve of in principle.
Unfortunately, not only is that not how the War Powers Act been used lately, both Bush and Obama set a precedent of ignoring Congress' lack of approval for their personal wars. Somehow I don't think Trump will be more prudent and humble than them.