Migrants are seen outside the U.S. Border Patrol McAllen Station in a makeshift encampment in McAllen, Texas, U.S., May 15, 2019. Reuters photos taken on Wednesday show adults and children outside the U.S. Border Patrol station for migrants in McAllen, Texas, sleeping on the ground and rigging up makeshift awnings with reflective blankets to shelter from the sun. REUTERS/Loren Elliott

Migrants are seen outside the U.S. Border Patrol McAllen Station in a makeshift encampment in McAllen, Texas, U.S., May 15, 2019. The photos, taken from a helicopter, also show people sleeping in a shaded area of a parking lot and crowded around a military tent. The ground temperature was about 89 Fahrenheit (32 Celsius) when the pictures were taken around midday. REUTERS/Loren Elliott

Migrants are seen outside the U.S. Border Patrol McAllen Station in a makeshift encampment in McAllen, Texas, U.S., May 15, 2019. Reuters photos taken on Wednesday show adults and children outside the U.S. Border Patrol station for migrants in McAllen, Texas, sleeping on the ground and rigging up makeshift awnings with reflective blankets to shelter from the sun. REUTERS/Loren Elliott

Migrants are seen outside the U.S. Border Patrol McAllen Station in a makeshift encampment in McAllen, Texas, U.S., May 15, 2019. The photos, taken from a helicopter, also show people sleeping in a shaded area of a parking lot and crowded around a military tent. The ground temperature was about 89 Fahrenheit (32 Celsius) when the pictures were taken around midday. REUTERS/Loren Elliott

Migrants are seen outside the U.S. Border Patrol McAllen Station in a makeshift encampment in McAllen, Texas, U.S., May 15, 2019. Reuters photos taken on Wednesday show adults and children outside the U.S. Border Patrol station for migrants in McAllen, Texas, sleeping on the ground and rigging up makeshift awnings with reflective blankets to shelter from the sun. REUTERS/Loren Elliott

Migrants are seen outside the U.S. Border Patrol McAllen Station in a makeshift encampment in McAllen, Texas, U.S., May 15, 2019. U.S. border officers apprehended nearly 99,000 people crossing the U.S. southern border in April, the highest monthly figure since 2007, Provost said. REUTERS/Loren Elliott