What constrains the Decider? As explained above, it's not the Constitution's requirement that Congress declare war. But, reading between the lines of the speech, maybe some limits can be discerned. The president emphasizes another source of authority, the "international mandate," the "writ of the UN security council,"--the sanction of the international "community." My Cato Institute colleague John Samples writes:
It is not just that this president, like others before him, ignored Article I of the Constitution. Nor is this president the first to shun moral complexity in favor of a Manichean outlook. President Obama is the first, however, to assert that his broad powers to initiate war should be limited primarily by people who are outside the American social compact.On this account, sotto voce, the Constitution is not just ignored. It is irrelevant.
For all his reliance on the first-person singular, in the speech, President Obama selectively employed the first person plural as well:
To brush aside America’s responsibility as a leader and – more profoundly – our responsibilities to our fellow human beings under such circumstances would have been a betrayal of who weare....
I want to be clear: The United States of America has done what we said we would do.
And here, the first-person plural is even more grating than the Royal "I". After all, "we"--the American people--were never asked.