Also the 2001 Authorization of The Use of Military Force, which has no expiry date, and allows unrestricted military action against anyone the administration believes played a role in the 9/11 attacks. As far as I’m awarel Trump has to do is claim Iran produced or sheltered terrorists at some point (even if it was in the past) and he’s more or less legally in the clear. There’s already precedent.

Under Presidents George W. Bush and Barack Obama, the 2001 AUMF was used to justify the deployment of US forces to Afghanistan, the Philippines, Georgia, Yemen, Djibouti, Kenya, Ethiopia, Eritrea, Iraq, and Somalia.

businessinsider.com/a-bill-to-repeal-the-aumf-jus…

Again, past decisions.