U.S. has been quietly helping Mexico with new, high-tech ways to fight opium

MEXICO CITY — In the past few opiate-soaked years, U.S. officials say, nearly all the heroin coursing through American cities has come from one place: Mexico.

U.S. authorities have expressed alarm at what they call an explosion of opium poppy in their southern neighbor. Echoing a federal drug agency assessment, President Trump has declared that “an astonishing 90 percent of the heroin in America comes from south of the border” and cited that as one reason to build a giant border wall.