In this Aug. 16, 2015 file photo, Sam Rainsy, leader of the opposition Cambodia National Rescue Party , waves from a car upon his arrival at Phnom Penh International Airport in Phnom Penh, Cambodia as hundreds of cheering supporters greeted him on his return from a trip abroad. The head of Cambodia’s opposition party has announced his resignation from the group after the country’s long-serving prime minister announced plans for a law that could lead to the party’s dissolution.