CAMBODIA HAS come a long way since the late 1970s, when the fanatical Khmer Rouge regime killed nearly 2 million of its own people. The country has enjoyed relative stability in recent years, aided by an economic growth rate that averaged nearly 10 percent annually between 1998 and 2008. Though Cambodian per-capita income is still among the lowest in Asia at only $1,000, the country has more than halved the share of its population living below the poverty line since 2007, according to the World Bank. The mortality rate of children under 5 years old has declined by two-thirds since 1998.

What Cambodia still lacks, however, is democracy. More than half of its resurgent population of 15 million is under 23, and the only ruler these Cambodians have known is Hun Sen, who rose to power in 1985 with the backing of Vietnam, which was occupying the country after ousting the Khmer Rouge. Though gentle by comparison with the Khmer Rouge — and still residually popular among beneficiaries of the country’s economic progress — Hun Sen is basically a dictator who relies on force, cronyism, electoral manipulation and external sponsorship to maintain power.

True, his foreign patron has changed over the past 28 years. Now it’s China, which uses military aid and economic investment to buy influence in Phnom Penh, as it once did in Burma. And just as they did for Burma’s military rulers, Chinese weapons and money have helped Hun Sen to fend off demands for greater freedom and political participation, whether they come from his own people or the United States and other Western nations.

That may be changing. Fueled by youth support, a democratic opposition party led by veteran activist Sam Rainsy stunned the regime in parliamentary elections in July. Hun Sen relied, as usual, on his party’s control over the country’s electoral machinery and used state media to spread propaganda about how an opposition victory would lead to civil war. Nevertheless, Sam Rainsy’s party doubled its seats in parliament, falling just seven short of the 62 needed for a majority — according to the official vote count, which Hun Sen’s partisans controlled and which Sam Rainsy plausibly describes as fraudulent.

All summer, the opposition has pressed its case for an independent investigation of the election, through the courts and through peaceful demonstrations in Phnom Penh. Hun Sen, characteristically, has deployed his police and military to intimidate his people, leading to a clash last Sunday in which one civilian was shot dead by police and many others were injured. Less characteristically, he has agreed to talk with Sam Rainsy.

The situation is tense; in the worst-case scenario, Cambodia’s ruler would launch a crackdown as crushing as the one with which Burma’s generals met a strong opposition showing in that country’s 1990 elections. At the moment, Sam Rainsy is negotiating with the regime — while pressuring it through demonstrations and a threatened boycott of the parliamentary session set to begin Monday. The hope is that his strong election showing at long last provides Cambodia’s people with enough leverage to start a peaceful democratic transition. In the struggle, Hun Sen will undoubtedly count on his old friends in Beijing. The United States must stand no less firmly for a democratic process.