(CNN) American warplanes are hard at work over Iraq and Syria, helping Iraqi army and Syrian rebel forces battle ISIS. In Iraq, American troops are busy training the military.

All of this is being done -- and will continue to be done -- without being officially sanctioned by Congress, although President Barack Obama now says he needs an Authorization for the Use of Military Force -- AUMF.

Passing AUMF legislation is Congress' way of giving the President permission to engage in prolonged military operations. Under the War Powers Resolution of 1973, the President can send U.S. forces into a conflict -- in this case airstrikes -- but must end those hostilities after 60 days unless Congress has given specific authorization.

The U.S. launched airstrikes in Iraq in August at the invitation of the Iraqi government, in part to protect American interests. That air campaign did not extend to Syria until September. In speaking to the American people about the fight against ISIS early that month, Obama said he had the authority he needed to act, but would welcome Congress' approval.

Read More