The War Powers Act of 1973, passed in the aftermath of the Vietnam War, puts limits on the ability of the President to send American troops into combat areas without Congressional approval.
Under the act, the President can only send combat troops into battle or into areas where ''imminent'' hostilities are likely, for 60 days without either a declaration of war by Congress or a specific Congressional mandate.
The President can extend the time the troops are in the combat area for 30 extra days, without Congressional approval, for a total of 90 days.
The act, however, does not specify what Congress can do if the President refuses to comply with the act. Congress could presumably suspend all funds for such troops and override a Presidential veto.-- N.Y. Times
Libya is the latest example of a President ignoring the War Powers Act. Turning command of Odyssey Dawn over to NATO seemed to imply US forces would be pulling out. Now National Security Advisor Tom Donilon has stated that US will continue military operations so long as Qaddafi continues attacking his own people. The statement does not even try to pretend the US is in a supporting role, it makes very clear the US is leading the way. It is almost as though killing Osama bin Laden has fueled the Obama Administration's desire to take out another terrorist leader (albeit one who also happens to be the rightful leader of a Muslim nation).
The problem is what happens after Qaddafi is either killed or steps down? We see with al Qaeda an almost renewed zeal in their commitment to attack the United States. We discover later that killing Osama bin Laden only solidified al Zawahiri's position as the undisputed leader. Getting rid of Qaddafi may allow an ever more despicable despot to have access to Libya's oil and wealth. The US track record for picking and supporting new regime leaders is unimpressive at best. From the Shah of Iran (backed by the US and implementer of the SAVAK) to the ineffectual Hamid Karzai, the US seems unable to understand the situation and find the right leader. Many would argue that is because the US is more concerned with how they will get along with the leader versus his domestic policies. No, that wasn't a politically incorrect statement. The US has not backed any female leaders of countries to replace ousted despots (at least not that I know. If you know of one, please post a comment about it).
The War Powers Act was in response to Nixon and his execution of the Vietnam War. In short, the WPA is an attempt to curb the President's ability to leave forces engaged in combat for extended periods of time costing the taxpayers money and using up critical military resources that may be desperately needed elsewhere.