(Washington Post) Nick Miroff Mary Beth Sheridan and Kevin Sieff Oct. 18 2019 at 7:37 a.m. A sudden increase in the number of Mexican families and asylum seekers trying to cross into the United States has raised fears of a new border crisis frustrating Department of Homeland Security officials who are unable to deter Mexican nationals with the same restrictive immigration policies designed to keep Central Americans out of the country. Mexico surpassed Guatemala and Honduras in August to again become the single-largest source of unauthorized migration to the United States according to administration officials who provided data on the Mexican migrants but were not authorized to speak about the situation publicly. In recent weeks thousands of Mexican adults and children have been camping out in queues at U.S. border crossings sleeping in tents while awaiting a chance to apply for safe refuge. Most concerning to U.S. authorities is the percentage of Mexicans declaring a fear of persecution or harm a claim that typically prevents their rapid deportation. Their requests for asylum are adding to the backlog of nearly one million pending cases in U.S. immigration courts and by law the United States must process their claims. Neither the government of Mexico nor the Trump administration has publicly acknowledged the sudden change a trend that threatens to shatter the fragile detente between the U.S. president and Mexican leader Andrs Manuel Lpez Obrador.