WHEN George W. Bush travels to Mexico to meet with Vicente Fox tomorrow, two significant trends-one positive, one negative-will clash. The first trend is the greater economic, political and ethnic integration of the United States and Mexico. The second trend is the greater threat to the United States from terrorism. While Mexico is not a haven for terrorists, its 2,100-mile border with the United States could be a significant portal for terror. Indeed, the tension between international economics and national security looms over America&#039s relationship with all countries of the world. Full Story