[SEJeff]

And this was formally updated post 9/11 with the AUMF (Acceptable Use of Military Force) which gave the president quite sweeping powers without direct congressional approval. The caveat is that the AUMF is only for 9/11 responsible countries or affiliates. Given 9/11 was Al Qaeda and they are Sunni, and that Iran is Shia, they are not actually related since they want to also kill each other. Still, these powers are being bastardizes to limit the authority of congress.

https://www.congress.gov/107/plaws/publ40/PLAW-107publ40.pdf

[adolph]

The AUMF was an addition to WP so Iran's lack of support for AQ doesn't limit normal WP operations. Additionally sectarian concerns are more malleable than presented. As an example review Iran's long-standing support for Hamas which is Sunni-affiliated.

  —Consistent with section 8(a)(1) of the War Powers Resolution, the Congress 
  declares that this section is intended to constitute specific statutory 
  authorization within the meaning of section 5(b) of the War Powers 
  Resolution.