A U.S. Border Patrol agent stands in front of the border fence that divides the U.S. and Mexico in San Diego, California, the United States, Nov. 17, 2018. Officers of the U.S. Customs and Border Protection (CBP) have tightened preparations at the U.S.-Mexico border in San Diego, California, for the arrival of massive caravans of Central American migrants. (Xinhua/Zhao Hanrong)