Here are two videos of then Senator Biden (both saying essentially the same thing) from 2007 where he makes it clear that starting a war against any country without congressional approval is an impeachable offense. Of course, that is if the country is not Libya and the President in power not one of his own kind!
Perhaps the silliest argument I have heard why this war is okay to fight without congressional approval is that it is being waged under a U.N. resolution. Since when has the U.S. surrendered its sovereignty to the international community? Moreover, any temporary latitude given to the Executive Branch deals with U.S. security being threatened as a result of inaction. This clearly is not the case.
And the 'humanitarian' reasons the President mentioned? Tell that to the relatives of the thousands of massacred Iranians in 2009 when there was at least an argument for U.S. national security (Iran being the prime exporter and financier of terror in Iraq and elsewhere today).
Enjoy the hypocrisy.