MEXICO CITY - Sidling up to migrants who arrive at the Tijuana airport and cruising the streets in border towns, "coyotes" in gold chains and dark sunglasses openly find customers for nightly scrambles across the U.S. border. Mexico's president offered to crack down on smuggling at a recent summit with President Bush. But close to 100 smuggling gangs are still operating, government officials say, in plain sight of Mexican law enforcement. "While drug smugglers are invisible for the most part, people smugglers are visible, working right in front of authorities," said Tijuana border expert Victor Clark, who has studied the...