"When did CAFTA become a treaty?"
when congress voted to give Bush "fast track" treaty negotiation authority.
Fast Track is about negotiating trade agreements and has nothing to do with treaties.
"Fast track does not dilute the power of Congress to regulate trade:
Under fast-track authority, trade agreements are submitted to Congress for an up or down vote under rules barring committee or floor amendments. Fast track does not give the President a blank check to negotiate trade agreements, nor does it undermine the constitutional prerogatives of Congress, which defines the objectives and limits of the President's negotiating authority in the legislation granting fast track. During any trade talks, the Administration must consult frequently with the House Ways and Means Committee, the Senate Finance Committee, and special advisers designated by Congress. Only Congress has the final say on any trade agreement negotiated by the President.
FWIW, some say CAFTA is technically not a 'treaty' per se, but rather an 'agreement'-- which means (probably) just that there's no ratification by the Senate. Check out post 274 of 322 by Paul Ross.
See Paul-- I am able learn something new once in a while.