Raúl Guillermo Rodríguez Castro, a grandson and close adviser to former Cuban leader Raúl Castro, attempted to send a letter directly to U.S. President Donald Trump bypassing traditional diplomatic channels, according to the Wall Street Journal. The letter reportedly included economic and investment proposals, requests for sanctions relief, and a warning that the Cuban government was preparing for a possible U.S. military operation. The back-channel effort failed when the Cuban businessman chosen as intermediary — a Havana-based luxury car rental and tourism entrepreneur — was turned away by border agents upon arriving in Miami. The initiative is seen as an attempt by those in Castro's inner circle to sidestep U.S. Secretary of State Marco Rubio, the son of Cuban immigrants and a long-time advocate of tougher measures against the island's government. Cuba has been struggling with a severe humanitarian and energy crisis after losing Venezuelan oil supplies following a U.S. military operation in Venezuela, with Mexico also halting shipments under U.S. pressure; the island received its first Russian oil tanker delivery in three months on 1 April.