 Thousands of Chinese nationals are among the half million migrants who used the gap last year. Most fly into South America before walking through the gap, eventually jumping on trains or buses in Mexico. The U.S. is now taking several steps to stop them. Ecuador this month began requiring visas for Chinese migrants. Mexico upped troop levels and began policing the rail yards. And this weekend, for the first time in six years, the U.S. deported 116 Chinese nationals back to China.