In fact, the whole history of hemispheric free trade reflects the fact that the U.S. legislature has been, with respect to those present, far more engaged and active on this issue than the Canadian legislature has been. Recall that the only reason we have any environmental or labour side agreements at all in any of these provisions is because the Democrats in the early 1990s insisted that they be part of what was then the contemplated agreement in NAFTA.
On May 26th, 2009. See this statement in context.