NAFTA hasn't failed
In the period of 1993–2004, total trade between the United States and its NAFTA partners increased 129.3% (110.1% with Canada and 100.9% with Mexico). It hasn't been as successful as some have hoped because the economic disparity between the US and Mexico is so great. That said, in Mexico poverty rates have fallen and real income risen, which undoubtly has some marginal effect on mitigating illegal immigration. In order to fully benefit from the agreement, Mexico must invest more in education and promote innovation in infrastructure and agriculture.
Keep in mind that NAFTA is a free trade agreement and not economic union. We're not all using the same currency in NAFTA, and there are still some trade barriers.