Testifying to the Senate Foreign Relations Committee, Secretary of State Rex Tillerson revealed that the US presence in Iraq is so permanent at this point that even if Iraq specifically requests the US withdraw and removes permission for them to be there, the US will remain.
Tillerson addressed the question from Sen. Tom Udall (D-NM), who asked whether the US intended to stay in Iraq uninvited like they are in Syria. Tillerson insisted the 2001 and 2002 Authorizations for Use of Military Force (AUMF) gave the US legal authority to stay.
This appears to be an entirely new position for the US government, as the Bush Administration agreed to withdraw from Iraq after being unable to get Iraqi authorization to stay, and absolute legal immunity for US troops along with it.
At this point, the US appears to be used to being engaged in overseas wars without permission, particularly in places like Syria, and having already declared their presence in Iraq to be permanently, officials figure they’re going to just pretend it’s legal.
It does bring up the question of US troops’ legal immunity from war crimes in places like Syria, where they’ve been deployed without permission or any assurances that they won’t be held liable for killings.