But by word of mouth, some have realized they can simply cross into U.S. territory, largely uninhibited by Mexican authorities. In twos or threes — occasionally by the dozen — they arrive at the border wall and manage to get over. Often within minutes, border officers quickly arrive to escort them to detention centers and begin “credible fear” interviews.

Over two nights last week, Associated Press journalists saw more than a dozen migrants taking the risk. A woman wearing a blue-beaded rosary waited with her children to see where they could cross. A Salvadoran migrant hid as he dug a hole in the sand under the wall. In the dark of night, migrants could be seen walking up a hill inside U.S. territory toward agents waiting to detain them.