Any case

Citing the War Powers Resolution, dissenters in Congress yesterday challenged President Obama's authority to engage in hostilities in Libya without their authorization. Legality here hinges on interpreting the vague resolution which, despite having been ignored time and again since its inception, seems to heartily support the current challenge: § 1543 defines applicable circumstance as, among other things,

... any case in which United States Armed Forces are introduced—(1) into hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances; (2) into the territory, airspace or waters of a foreign nation, while equipped for combat, except for deployments which relate solely to supply, replacement, repair, or training of such forces ...

Any case? Points for critics of the administration.

But Harold Koh, State Department legal adviser, counters that "the limited nature of this particular mission is not the kind of ‘hostilities’ envisioned by the War Powers Resolution.” Moreover, this is NATO's mission now--since at least April 7--and the US only lends support and not manned armed force.

The decades-long trend shows the Executive branch gaining power. Hard to imagine any check on that now.