Things are hard enough for the Obama Administration when it has logic, the national interest, and Democratic party principles on its side. As, in my view, has been the case with its health-care reform effort, the campaign to limit the Bush tax cuts to the bottom 95% or so of the income distribution, the opposition to the "brave" and "serious" Ryan/Republican budget plan, the ongoing struggle over the debt ceiling, and so on.
Given those built-in obstacles, it has no need -- and can barely afford -- to invite needless trouble for itself, as it has with its inexplicably stubborn and short-sighted approach toward Congress on the Libya campaign.
Lawyers can argue, and evidently they did, about whether as a technical matter the Administration "had to" get Congressional approval for "hostilities" of this sort. But as a matter of politics in both the short-term and the broad historical sweep, of course the Administration absolutely had to involve the Congress. Short-term, by getting Congressional "buy-in" it would have buffered itself against the kind of rebuke it has now suffered. In the long historical view, it would have helped correct the drift toward unaccountable war-making power that candidate Obama himself was so eloquent in denouncing.