The U.S. withdrawal from the Trans-Pacific Partnership (TPP) has affected the prospects of mega-regional trade agreements (MRTAs) in the transpacific and transatlantic. In the Asian Pacific, negotiations for the Regional Comprehensive Economic Partnership (RCEP) might accelerate. It is also plausible that 11 other TPP signatories decide to implement TPP sans US. The objective of this paper is to estimate economic welfare effects of alternative sequencings of MRTAs for the Asia-Pacific countries using a dynamic computable general equilibrium (CGE) model. Our results suggest that the United States loses an opportunity to gain 0.7% in its economic welfare by 2034 when the TPP is never implemented, and that its welfare gain will be reduced by 0.3 percentage point when its participation in the TPP is delayed by five years.