Under the War Powers Act, Congress is supposed to vote on any war within 60 days of its launch. The ISIS war began in 2014, and because of mid-term elections looming large, Congress just never voted on it, meaning the war was never authorized.
There’ve been a few pushes for Authorizations for the Use of Military Force (AUMF) against ISIS, but they’ve never gotten far. beyond their respective committees. The administration has simply ignored the lack of authorization for the war so far, but deploying ground troops into Syria is likely to bring the question some new attention.
This is doubly true because, back when those AUMF proposals were making the rounds, endorsed by the White House, they almost all explicitly banned sending ground troops into Syria, meaning even if the administration had gotten their requested authorization, they’d be violating it now.
That also means even if, as some Congressmen hope, the deployment obliges the Congressional leadership to finally see the AUMF brought to a vote, they’re likely going to have to pen a brand new version of the authorization that’s even broader, in keeping with the various ways the war has expanded in recent weeks.
Those escalations in the war probably aren’t done either, so the administration’s input on any new draft will be an interesting guide into their future plans, and another reason why the White House is hoping this new push for authorization, like previous pushes, is brief and uneventful.