Jack Goldsmith weighs in on whether, in the absence of further congressional authorization, the President may pull another Harold Koh and claim we are not engaged in hostilities in Iraq:

Several readers write to note that another reason to seek congressional authorization now is to avoid the implications of the War Powers Resolution later.  The WPR requires the administration to get approval from Congress 60 (or 90) days after “hostilities” in Iraq begin – i.e. October or November.  The administration might argue that it is not engaged in “hostilities” within the meaning of the WPR, as it did in connection with the Libya bombings.  But that claim was unpersuasive (my arguments why are here and here, but many others reached the same conclusion).  Moreover, most of the criteria in the administration’s fullest articulation of why the WPR did not apply in Libya might cut the other way in Iraq and Syria – namely, the mission is not limited, the exposure of our armed forces might not be limited, the risk of escalation is probably not limited, and the military means deployed might not be limited.  So the administration’s already-flimsy rationale for circumventing the WPR in Libya will be even harder to assert in Iraq/Syria.

In any event, come October, Congress will have to get involved.

Bobby Chesney has more on what an AUMF for ISL would look like.