The United States had already concluded a free trade agreement (FTA) with Canada in 1988, but the addition of a less developed country like Mexico was unprecedented. Opponents of NAFTA have picked up the wage gap with Mexico, which had a per capita income of only 30 percent [PDF] of the United States. U.S. presidential candidate Ross Perot argued in 1992 that trade liberalization would result in a “huge suction noise” from the United States.