Jeffrey Wasserstrom teaches at UC Irvine and is the author of "China in the 21st Century: What Everyone Needs to Know."

In July, two stories out of China were big news. One focused on watermelon seller Deng Zhengjia, a poor urban migrant in Hunan province, who became newsworthy only when reports circulated that thuggish chengguan — members of para-police units — allegedly beat him to death. A week later, someone very different, Bo Xilai, was back in the news when he was formally charged with "abuses of power" and corruption. Bo — the former party boss of one of China's biggest cities, Chongqing, a Politburo member and once thought to be bound for elevation to the Communist Party's ruling Standing Committee — was anything but poor, powerless or unknown before cascading scandals brought him down in 2012. Putting the tales of Deng's death and Bo's indictment side by side illuminates a major challenge China's leaders face: How to keep the people believing the stories they tell to justify their rule.

In China, as elsewhere, such stories often involve a kind of political-product differentiation that presents the current era as totally unlike earlier dark periods. This meant that, during the Mao Tse-tung years (1949-1976), a steady stream of propaganda stressed the allegedly total contrasts between the new China of the Communists and the old one of Nationalist times (1927-1949). Nationalist leader Chiang Kai-shek was presented as obsessed with vanquishing his rivals and being closely allied with thugs and gangsters who rode roughshod over ordinary people and were rewarded for it. The Nationalist Party was portrayed as corrupt and dominated by cliques, many of whose members were close friends or relatives of one another.

In the post-Mao reform era, versions of this story continue to be told, but leaders also stress a newer one that contrasts the present age to the chaotic Cultural Revolution decade (1966-1976). Since Mao's death, this tale goes, China has not just boomed economically but has been placed on a more stable, saner political footing, thanks to the end of bitter factional infighting and scattershot purges....