The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all... ~ NATO treaty, Article 5The NATO war in Afghanistan, however badly it has been run, can be justified as a defensive response to the 9-11 attacks by the al Qaeda/Taliban alliance upon the United States. Libya is different.
There was no attack against any of the 28 member countries. Libya isn't even in Europe. NATO claims it is acting to implement UN Security Council Resolution 1973, specifically clause 4 "protecting civilians and civilian populated areas under threat of attack." However, even NATO does not try to justify their actions within the wording of the NATO charter. So while individual nations may choose to attack Libya and even use the NATO command structure to coordinate those attacks there is absolutely no treaty obligation requiring participation.
Which leads us to the War Powers Act. The United States is under no legal treaty obligation to assist NATO in the Libyan Adventure. Under the War Powers Act the US can provide munitions, logistical, and intelligence assistance under Presidential discretion without permission of Congress. But, American combat operations over Libya, including armed drones, constitutes acts of war requiring Congressional approval.
Continuing those operations into today without Congressional action violates United States law. Period. And, yes, that is an impeachable offense.