The amendment uses the term of art "Cruel, inhuman or degrading treatment." There is TONS of law on the subject, and it is not a trivial matter to ascertain how the McCain amendment alters existing structure.
[JURIST] AP is reporting that the White House has agreed to accept the McCain Amendment [JURIST document] that would ban the cruel and inhumane treatment of terror detainees, according to congressional officials. The White House has previously threatened to veto any legislation to which the amendment was attached and called for an exemption for CIA operatives.
I'm sure it's not easy to determine whether this really impacts current legalities pertaining to torture; if you see an explanation that makes sense of this bill, could you please ping me? Thanks.