CARACAS, Venezuela — President Donald Trump said Tuesday that the United States had nothing to do with an alleged incursion into Venezuela that landed two U.S. citizens behind bars in the crisis-stricken South American nation. Trump said he had just learned of the detention of the pair, accused by Venezuela of being mercenaries. Venezuelan President Nicolás Maduro said they were part of an operation to kill him that was backed by neighboring Colombia and the United States. “Whatever it is, we’ll let you know,” Trump told reporters in Washington before departing from the White House to Arizona. “But it has...