CHOEUNG PREY COMMUNE, Kompong Cham Province – At 7:50 a.m., the prime minister’s helicopter circled this rural village in Kompong Cham province. Soon after, a convoy of SUVs pulled up to the colorfully adorned Kiri Monisavorn pagoda and Mr. Hun Sen walked in with two-dozen security guards and a band of senior government officials. Some 5,000 people had been trucked in Monday from Batheay district to watch Mr. Hun Sen’s speech—his last nationally broadcast remarks before stepping out of the spotlight during the official monthlong election campaign season that starts Thursday.