The NYT has an op-ed piece by Bruce Ackerman that opens with these words:
PRESIDENT OBAMA’s declaration of war against the terrorist group known as the Islamic State in Iraq and Syria marks a decisive break in the American constitutional tradition. Nothing attempted by his predecessor, George W. Bush, remotely compares in imperial hubris.
Mr. Bush gained explicit congressional consent for his invasions of Afghanistan and Iraq. In contrast, the Obama administration has not even published a legal opinion attempting to justify the president’s assertion of unilateral war-making authority. This is because no serious opinion can be written.
Read the whole thing.