What would happen if NAFTA were renegotiated?

Robert Lawrence of the Peterson Institute has some thoughts (Much Ado about NAFTA, Guardian, March 7):

What would be the consequences if NAFTA were to be renegotiated?... Aside from the indignity of being pressured, Canada and Mexico would probably agree to the language with respect to labor and environment that the United States would be able to demand without alienating the Republicans who are the mainstay of support for trade agreements. After all, because of opposition from states that are tough on trade unions, the United States has ratified only two of the eight core conventions of the International Labor Organization while Canada has ratified five conventions and Mexico six. And unlike the United States, the other members of NAFTA still participate in the Kyoto protocols on climate change. Moreover NAFTA is popular in Mexico and Canada, and both countries might see new negotiations as a way to promote their ideas for deepening economic integration in North America. Mexico, for example, would surely like an improved treatment for the movement of labor, while Canada would like to replace US antidumping provisions with antitrust rules.

...The renegotiation proposals create uncertainty about US commitments to its existing trade agreements and raise the risk that the renegotiated agreements could be rejected. The full benefits from trade agreements are only realized when they are credible and provide a permanent and reliable set of rules of the game that private decision makers can count on.

If NAFTA is renegotiated, it will immediately call other US agreements into question. Why shouldn't the Central American agreement (CAFTA) be reopened on similar grounds? What about the US-Israel agreement, which was negotiated so long ago that it doesn't have any labor or environmental provisions at all?