TOKYO -- Chinese President Xi Jinping is now shifting his focus from the battle against the novel coronavirus back to the war against what he regards as an equally dangerous presence: his political enemies.

Over the weekend, it was announced that Sun Lijun, a 51-year-old vice minister at the Ministry of Public Security, which oversees China's police organizations, is being investigated by the country's main anti-corruption bodies, the Chinese Communist Party's Central Commission for Discipline Inspection and the National Supervisory Commission.

"Two vice ministers of public security have now fallen from power in one and a half years," a veteran party member said, describing the significance. "And to do it now, amid these current circumstances?

"It shows that the top leader's interest is not limited to epidemic prevention and the economy. It also shows how difficult it is to take full control of the public security sector."

Sun was in charge of a highly sensitive area within the police force. He handled "domestic security," the most important element of public security, and dealt with classified information related to maintaining stability. This is why his background has so far been largely kept under wraps.

Sun Lijun at a meeting in Wuhan on April 7. The vice minister of public security is now under investigation by the party's disciplinary watchdog. © AP

Sun is also a specialist in the field of public health. Roughly 20 years ago, he received a scholarship from the World Health Organization and studied at and obtained a master's degree in public health from Australia's University of New South Wales, the second-largest university in Sydney.

As a public health expert, Sun was part of a coronavirus investigation team dispatched to Wuhan by the central government. While in Wuhan on March 5, Sun attended a party entrance ceremony for female police cadets.

At that point, Sun knew nothing about his political fortunes. Everything seemed fine; he was smoothly carrying out his duties. But a secret investigation into his alleged misconduct had been underway since last year.

On Friday, two days before Sun's fall from grace, gross domestic product data for the January-March quarter was announced, showing China's economic growth had plunged into negative territory for the first time since 1992, marking a 6.8% contraction.

That night, the party's powerful 25-member Politburo held a meeting. Increased testing for COVID-19 was on the agenda as was taking measures to guard against a rebound of the virus. The leaders also discussed ways to stimulate consumer spending.

But the most important item on the docket was expressed in the last sentence of the Politburo statement: "The meeting also studied other matters."

"Other matters" pointed to the disciplinary measures taken against Vice Minister Sun.

On Sunday night, when Sun's purge was finalized, Public Security Minister Zhao Kezhi gathered the top leaders of the ministry to explain what had happened. There, Zhao ripped his long-time subordinate with piercing words.

The investigations into Sun Lijun were "an inevitable result of his long-standing disregard of the party's political discipline and political rules, his failure to observe discipline, rules, [and for his displaying a lack of] awe and wanton behavior," the meeting concluded, according to the ministry's website.

The lack of "awe" was no doubt a criticism of Sun's attitude toward Xi, the "core" of the party.

The meeting called for a "pure" police team. We must "resolutely remove the black sheep" from the police team, the members agreed.

Vice Minister of Public Security Meng Hongwei fell afoul of Xi Jinping's adminisrtration in 2018. In this photo from 2016, he is delivering a campaign speech at Interpol's 85th session of the general assembly, in Bali, Indonesia. © Xinhua/ AP

The other vice minister of public security to fall from grace was Meng Hongwei. In October 2018 it was announced that Meng, who doubled as the president of the Lyon, France-based International Criminal Police Organization, was under investigation.

While keeping the top-level post at the ministry back home, Meng in 2016 became the first Chinese head of Interpol, managing the agency's relations with its 190 member countries and regions.

Meng went missing during a temporary return to China, prompting his family in Lyon to report his disappearance to French police.

Interpol descended into chaos at the sudden disappearance of its president. But the Xi administration was acting on a political motive.

In the summer of 2018, China's political situation had been shaken by a power struggle within the party. Months earlier, in March, Xi pushed through a revision to the national constitution that allows him to remain as president indefinitely. But the hasty move, combined with what seemed to be at least a willingness to tolerate "a personality cult" being built around him, drew a strong backlash from within the party.

The Xi camp launched counterattacks, which included enforcing strict official discipline within police organizations that had not completely yielded to Xi's authority.

Meng was ultimately sentenced to 13 years and six months in jail -- a ruling that came three months ago, immediately before Wuhan was locked down.

"In the process of Meng being punished," a source ventured, "a secret investigation into Sun might have also begun."

Meng and Sun were close to Zhou Yongkang, China's former security czar who was a Politburo Standing Committee member. Zhou was sentenced to life in prison after being targeted by Xi's anti-corruption campaign. Meng served Zhou for years.

Meng and Sun became the first and second victims of a crackdown on Zhou's henchmen within the police organizations.

This was also made clear at the meeting of senior Ministry of Public Security officials chaired by Minister Zhao Kezhi on Sunday night. "It is necessary," the participants agreed, to "effectively eliminate the influence of Zhou Yongkang, Meng Hongwei, Sun Lijun and others from the ideological, political, organizational and work style."

The fate of one more figure remains in question: Zhou Yongkang's successor as security czar, Meng Jianzhu.

Meng Jianzhu, a former Politburo member, is now retired, but it is widely known that Sun was close to him, serving as a de facto personal secretary.

Meng Jianzhu in Sydney in 2017. The retired Meng belongs to the "Shanghai faction," a group of people close to former President Jiang Zemin, and his destiny is key to China's ongoing power struggle. © AP

Meng Jianzhu belongs to the "Shanghai faction," a group of people close to former President Jiang Zemin, and his destiny is seen as a litmus test of the power struggle.

That likely comes down to how much of a grip one Xi ally in the police force continues to hold. Wang Xiaohong, the most senior vice minister of public security is a key figure in the Xi camp and an old friend of Xi's.

Wang belongs to Xi's network of personal connections in Fujian Province, where the Chinese president once worked.

Although an outsider in the ministry, Wang's connection to Xi gives him special status.

Many pundits think retired persons like Meng Jianzhu will probably not be accused of any misconduct if Wang manages to keep control of public security and police organizations. If his influence wanes, expect to see more disciplinary action to shore up Xi's status.

The president's power struggle is far from over. With two years left before important personnel changes are made at the party's next national congress, Xi will have to keep wielding his anti-corruption campaign.

Xi visited Shaanxi Province on Monday. His inspection tour of the northwestern province followed a similar recent trip to the coastal province of Zhejiang. Shaanxi is important to Xi, one of the "second-generation reds," or children of revolutionary-era party leaders.

President Xi Jinping visits students at a primary school in Laoxian township, in the city of Ankang, Shaanxi Province. Xi spent part of the 1966-1976 Cultural Revolution in a farming village in Shaanxi. © AP

Xi Zhongxun, the president's late father who rose to vice premier, was born in Shaanxi's Fuping County. A vast mausoleum park has been constructed there in memory of the elder Xi's achievements.

The younger Xi himself lived in a farming village in Shaanxi for a long period of time during the 1966-1976 Cultural Revolution. It was also in Shaanxi that he got to know and deepened his bond with Wang Qishan, now the country's vice president.

Shaanxi is also the stronghold of the "Xi faction," along with Zhejiang, where he once served as the top local official. Under the Xi administration, many people related to Shaanxi have been promoted to key posts.

They have formed the "Shaanxi faction" and support the "Zhejiang faction," the core of the Xi faction.

Xi's harsh clampdown on resistance forces within the public security and police organizations and his "pilgrimages" to the two main strongholds are likely to have great political meaning.