Vietnam would be the biggest benefactor in the TPP. Tyler Cowen, a prolific economist, makes the case that the benefit to Vietnam would be so huge that any costs borne by U.S. interest groups and constituencies are marginal.(http://thediplomat.com/2015/04/trans-pacific-partnership-do-it-for-vietnam/)
The economic reason is simple as TPP at its core is a tariff effacing trade agreement. As Vietnam does a lot of trade with the United States and TPP will slash major trade protections, it follows that Vietnamese goods will be particularly competitive in a post-TPP context.
TPP would likely facilitate the ongoing strategic rapprochement between the United States and Vietnam like late last year where the US lifted its long-standing arms embargo on Vietnam leading to closer ties. One of the United State’s grand strategic goals is to uphold the liberal economic order after the Second World War. Cowen notes that TPP would inspire broader freedom for Vietnam’s residents.
There is an American national interest case to be made for enhancing the economic welfare of Vietnam and ensuring that the country has a stake in a formal liberal economic order, but it is not one that will resonate with the primary U.S. critics of the TPP who continue to be primarily concerned about the agreement’s distortionary effects on U.S. workers and its perceived tilt toward the interests of large corporations.