Pretending "a new war" is afoot only if U.S. infantrymen put "boots on the ground" does not make it so. Obama is right now preparing a new war: a sustained, lethal campaign against a distinct enemy that America has not fought before. Ross Douthat makes the most persuasive case I've yet encountered favoring such a war. Its opponents counsel that the whole history of U.S. intervention in Iraq suggests we haven't any ability to competently or successfully shape events there, nor any clue what intervening in the present crisis will bring.
I'll weigh and comment on various arguments in due course.
What ought to be clear for now, whether one believes Obama's new war plans to be wise or imprudent, is that Congress ought to decide whether or not America commits to them, not a lame-duck president acting beyond his constitutional authority and without debate. Using air power to protect refugees on a mountain from immediate slaughter, or to stop rebels from unexpectedly overrunning American diplomats, are plausible examples of times when emergencies justify quick executive responses. Yet as Glenn Greenwald notes, American presidents have been known to increase their own power by ginning up or exploiting emergencies. Obama is on the precipice of this sort of exploitation. A lengthy intervention in a foreign civil war is at the other end of the emergency spectrum from an unexpected rescue, yet Obama uses the emergency to justify the months-long campaign.
It is not too late to change course.
The legal and political cases for Obama going to Congress are strong, says Jack Goldsmith, harkening back to the president's decision to seek input before intervening in Syria. He cites Obama's words about that decision (my emphasis added):
I have decided that the United States should take military action against Syrian regime targets. This would not be an open-ended intervention. We would not put boots on the ground. Instead, our action would be designed to be limited in duration and scope .... But having made my decision as Commander-in-Chief based on what I am convinced is our national security interests, I’m also mindful that I’m the President of the world’s oldest constitutional democracy. I’ve long believed that our power is rooted not just in our military might, but in our example as a government of the people, by the people, and for the people. And that’s why I’ve made a second decision: I will seek authorization for the use of force from the American people’s representatives in Congress ....
My administration stands ready to provide every member with the information they need to understand what happened in Syria and why it has such profound implications for America’s national security. All of us should be accountable as we move forward, and that can only be accomplished with a vote ....
Yet, while I believe I have the authority to carry out this military action without specific congressional authorization, I know that the country will be stronger if we take this course, and our actions will be even more effective. We should have this debate, because the issues are too big for business as usual ....
A country faces few decisions as grave as using military force, even when that force is limited. I respect the views of those who call for caution, particularly as our country emerges from a time of war that I was elected in part to end .... So just as I will take this case to Congress, I will also deliver this message to the world .... We all know there are no easy options. But I wasn’t elected to avoid hard decisions. And neither were the members of the House and the Senate. I’ve told you what I believe, that our security and our values demand that we cannot turn away from the massacre of countless civilians with chemical weapons. And our democracy is stronger when the President and the people’s representatives stand together.
Says Goldsmith, "The logic of the President’s speech last year so obviously applies to the Iraq situation that if he does not now seek congressional authorization, one might reasonably question his sincerity last August—as many did at the time."