A cargo ship navigates through the Panama Canal, seen from the Cerro Ancon in Panama City. (Matias Delacroix | AP)UNITED NATIONS — The United States and China clashed over the Panama Canal at the United Nations on Monday, with the U.S. warning that Beijing’s influence over the key waterway could threaten global trade and security and China calling U.S. accusations a pretext to take over the canal. The Panama Canal needs more water. The Panama Canal Authority says the dam solves a long-term water shortage problem. Ambassador Dorothy Shea, who spoke afterward, went after China, expressing concern about its “outsized influence over the Panama Canal area, especially over critical infrastructure and port operations.”Is Trump’s rhetoric on Greenland, Canada and Panama Canal a ‘Madman Strategy’?