Unlike Libya in 2011, the U.N. did not have a resolution permitting President Obama to launch offensive military attacks inside a foreign and sovereign nation, Syria. Without a U.N. resolution there was no international law permitting President Obama to attack ISIS inside Syria.
Without a legal basis in international law, President Obama needs to use U.S. law for his Syria ISIS campaign.
So unlike Libya in 2011, and absent of international law to support the legality, for his 2014 Syria attacks to be legal President Obama needed to use US law; specifically, the War Powers Act.
President Obama is using two constructs. #1) The War Powers Act -and- #2) AUMF The 9-11-01 Authorization for the Use of Military Force.
But there’s a catch or two.
First, because President Obama is going to use the War Powers Act, and is not acting to defend the U.S. homeland, and is engaging in offensive military actions, he has to notify congress in writing immediately – and then update in writing within 30 days. It’s how the law works. But note what’s missing.
AUMF letter
There is no mention of ISIS, because legally there can’t be. In order for Obama to use the 2001 AUMF he has to be attacking “al-Qaeda”, specifically “al-Qaeda”.
The AUMF only applies to al-Qaeda, not ISIS or any other group or state