The original Korea-U.S. FTA agreement was signed in time (July 1, 2007) to qualify for expedited consideration by Congress under Trade Promotion Authority (TPA or fast track). But this supplemental agreement, which changes specific elements of the original, was not.
Scott Lincicome lays out options, with their shortcomings, here: KORUS and TPA, ctd. Highly recommended. It's apparent there's no bullet-proof way forward.