Zhou Yongkang, China’s former domestic security chief, is under investigation as part of an anti-corruption drive. (Jason Lee/Reuters)

The ruling Communist Party on Tuesday announced an investigation of the country’s former domestic security chief, Zhou Yongkang, sending tremors through China’s political world and signaling that an anti-corruption drive is now reaching previously untouchable levels of the leadership.

If found guilty — as most officials are in such cases — Zhou would be the highest-ranking Chinese party leader to be taken down in more than two decades.

The move reflects the tenacity of President Xi Jinping’s anti-corruption drive, but also his willingness to assume political risks. By targeting Zhou, Xi is breaking an unwritten rule against investigating current or former members of the Standing Committee, the party’s highest circle of leaders.

Tuesday’s announcement revealed how thoroughly Xi has consolidated his power since taking over the party in 2012.

“You can continue to speculate on so much else about the party, but no one will question the fact that Xi is now fully in charge,” said Robert Kuhn, a businessman who has personal ties with many senior Chinese leaders.

The Chinese leadership’s decision to investigate Zhou Yongkang is an unusual move against a current or former member of the Standing Committee, the Communist Party’s highest circle of leaders. (Feng Li/Getty Images)

Xi’s anti-corruption drive has been the most far-reaching and sustained in China’s modern history. But it risks generating a backlash from various party factions on whose support he depends to rule. Some party members fear that the Zhou case raises the possibility of future investigations into their own patrons and former top leaders.

Already, Xi’s administration has put the military on notice that even that powerful institution is not immune to scrutiny, expelling one of China’s top retired military leaders, Xu Caihou, earlier this month for alleged graft.

Relatives of a key ally of former president Hu Jintao have also been arrested, sparking speculation that Hu’s political faction is next.

Xi is “not just cutting off access to the goodies and perks of lower-level officials. He’s striking at every major power in the party,” said Chris Johnson, former top China analyst for the CIA. To get other party leaders to sign off on the moves, Xi has argued that he is acting to ensure the survival of the party, which is under fire from the Chinese public for its blatant graft.

“You look at the moves he’s making here and in foreign policy, and a picture’s emerging that this is a guy who sees himself in almost messianic terms, sent to save the party,” said Johnson. “Amid the corruption, he sees himself as the one with clean hands.”

Heavy sentences expected

Although the worst official punishment that can be meted out in such internal investigations is booting cadres from the party, the probes are then often transferred to the judicial branch, where the expelled officials inevitably are convicted of crimes and receive heavy sentences.

Rumors had been swirling for two years of a carefully managed plan to eject Zhou from the party and strip him of his power.

As Xi’s targets go, Zhou was particularly vulnerable, at least in one aspect. The stone-faced politician has long been one of China’s most unpopular senior officials.

He built the country’s domestic security system into a feared, sprawling apparatus — first as head of the Ministry of Public Security, then as the overseer of its police, courts, prosecutorial system and domestic intelligence work.

While Zhou was in that position, China’s spending on domestic security exceeded even its defense budget. With those resources, he cultivated considerable influence and allies. Meanwhile, through his connections with the oil sector, where he had also held official positions, he is suspected of having accumulated significant wealth.

There were signs as early as 2012 of the growing discomfort within the party with the power Zhou had amassed. Zhou’s successor as security czar was not given a seat on the ruling Standing Committee when Xi and a new generation of top leaders were introduced.

The sensational trial of former high-ranking party leader Bo Xilai was also seen as a knock against Zhou, who had been Bo’s longtime patron. Bo was convicted last year on corruption charges.

But the fact that it took almost two years to open a case against Zhou shows the stakes involved in taking him on. Such probes are carried out by secretive internal party investigators. In rare interviews, investigators have said it is necessary to carefully build strong evidence — often by extracting confessions from a target’s underlings — to convince party factions to approve of a sensitive case.

Bo remained defiant even after he was sentenced to life in prison on the corruption charges. Willy Lam, a political analyst in Hong Kong, said that Zhou was more likely to cooperate with investigators trying to prove his guilt, for the sake of his son and other relatives long rumored to be under detention while a case was assembled against the former security czar.

The announcement of Zhou’s investigation came in a terse statement by the state-run Xinhua News Agency saying that he was suspected of “serious disciplinary violations.” It gave no details. Notably missing from the announcement was the honorific “comrade” — sometimes a sign an official has been pushed out of the party.

A high-stakes strategy

In the cutthroat world of party politics, attacking Zhou is in many ways an act of self-preservation for Xi and his agenda, said Zhang Lifan, an historian in Beijing. “If he does not tackle this tiger, he will be eaten up the group of tigers,” Zhang said. “But just because he has tackled one tiger does not mean he is safe. He must keep going.”

If Xi stops the anti-corruption campaign, he risks leaving the perception among the public and within the party that it was largely an exercise to shove aside political rivals, many analysts say.

Some analysts say Xi is already taking measures to protect himself from such criticism by framing Zhou’s investigation as part of a broader institutional reform process. They note Tuesday’s news was paired with an announcement that top party leaders would meet in October to discuss the promotion of the rule of law — something human-rights groups say China is woefully lacking.

“It’s a way to steer the narrative away from this criticism of Xi as an authoritarian, megalomaniacal Mao figure, and casting his actions, including [the investigation of ] Zhou, as moves toward saving and changing the party,” Johnson said.

One key question in Zhou’s case is whether he will be charged with financial crimes, as many expect, or far more serious political ones as well — such as a widely rumored attempt at a power grab against Xi, analysts say. They say such political charges are unlikely, because they risk damaging the party’s image and exposing internal party struggles and divisions.

“Of course they won’t fully disclose the Zhou case,” said Li Datong, a political analyst and former editor at a state-run newspaper. Li has argued that Xi’s anti-corruption campaign is simply window dressing to cover up the party’s deeply rooted, intractable problems of graft and abuse of power.

“It’s not just individual officials like Zhou who are corrupt; it’s the entire system,” he said. “But the true situation is too ugly to be made public.”

Xu Yangjingjing, Gu Jinglu and Xu Jing contributed to this report.