Daily Digit is the story behind the numbers that make our world work. Today we’re looking at the advancing migrant caravan. According to U.S. defense officials, President Trump’s move to send troops to the U.S.-Mexico border could cost taxpayers $220 million. This figure could change depending on the size and scope of the mission. The Department of Defense estimates that 7,000 troops will be placed in California, Arizona and Texas in order to stop a caravan of 3,500 Central Americans seeking asylum, but President Trump has said he wants to send 15,000 troops to the border. The president has referred to the caravan as an “invasion”; however, a Pentagon risk assessment reportedly found that the caravan did not pose a threat to the United States.