Eagle Pass, Texas — By 6:30 a.m., there were scores of migrants, including parents carrying young children and babies, between a seemingly endless line of razor wire and the Rio Grande, pleading with Texas National Guardsmen to grant them safe passage into the U.S. "Please, let us through," a woman in the river clamored in Spanish. "Let us pass," another migrant yelled. "There are kids in the water," a man said. These dire scenes have become a daily occurrence near the Texas border town of Eagle Pass, now the busiest sector for illegal crossings alongside the remote Tucson sector in...