4. Under what circumstances is it constitutional to try persons before military tribunals? Was it constitutional to try southern-sympathizers involved in John Wilkes Booth's plot on President Lincoln and other high government officials? Does it matter whether the plotters had connections with the Confederate Secret Service? Three hundred Dakota warriors were sentenced to death in 1862 by a military tribunal for their role in an uprising against Minnesota settlers--was that constitutional? Would it be constitutional to try by military tribunal an American citizen found to have participated in the World Trade Center attack? A Canadian citizen?

The Constitution divides war powers between the Congress and the President.  This division was intended by the framers to ensure that wars would not be entered into easily: it takes two keys, not one, to start the engine of war.  

Explanation:

The Constitution's division of powers leaves the President with some exclusive powers as Commander-in-Chief (such as decisions on the field of battle), Congress with certain other exclusive powers (such as the ability to declare war and appropriate dollars to support the war effort), and a sort of "twilight zone" of concurrent powers.  In the zone of concurrent powers, the Congress might effectively limit presidential power, but in the absence of express congressional limitations the President is free to act.  Although on paper it might appear that the powers of Congress with respect to war are more dominant, the reality is that Presidential power has been more important--in part due to the modern need for quick responses to foreign threats and in part due to the many-headed nature of Congress.