In the wake of Viet Nam, it became obvious that World War II would be the last declared war. For political reasons, Korea and Viet Nam were never declared. In an effort to escape blame for an unpopular war, Congress pointed at the Presidency and essentially said, "He did it." The public was supposed to infer that Congress's hands were clean because they had not actually approved the war.
At the same time, they passed the War Powers Act in an effort to stop future Viet Nam's. The idea was that the President could not start a conflict and allow it to drag on indefinitely on his own authority. He had to get Congressional approval. To allow for emergencies, the President was allowed 60-90 days to get the approval.
President Nixon vetoed the act but it was passed over his veto. Since then, every president who engaged in protracted hostilities (Reagan, both Bushes, and Clinton) at least paid lip service to the act.
Depending on your reading of it, the law may infringe on the President's authority as commander in chief. Regardless, it provides convenient political cover in case a conflict turns sour. George W. Bush was able to point to leading Democrats' votes authorizing the invasion of Iraq.
We are passed the point in Libya where President Obama should have made his pitch to Congress and asked for authorization to continue the action. His reason for not doing this was that American servicemen are not actually in danger so this does not count as hostilities. In taking this stand, he ignored the advice of a team of lawyers.
This is the part that confuses me. It is pretty much a given that Obama could have a resolution supporting the action in Libya if he asked for one. So why didn't he? Why is he using twisted logic to justify going alone?
There are several ways that Libya could go wrong politically. The current stalemate could continue allowing Gaddafi to stay in power after Obama said that he must go. Gaddafi could mount a new offensive, suppressing the rebels and, again staying in power. Or the worst could happen and Gaddafi's government could disintegrate leaving us with yet another nation to rebuild. The ideal resolution, Gaddafi leaving office but leaving behind a strong enough government to assure honest elections, is unlikely.
Clearly it would be in President Obama's best interests to have some prominent Republicans vote in favor of continued operations. That could neutralize what could otherwise turn into a major issue in next year's campaign. It is also giving the Republicans a chance to distance themselves from the Bush-era image as a the party of war-mongers.
In the meantime, even Democrats and liberals are attacking Obama on his failure to comply with the War Powers Act. Unless he acts soon this will become a millstone around his neck.