Chinese President Xi Jinping in Pretoria, South Africa, on July 24. (Themba Hadebe/AP)

WENGUANG SUN, a retired university professor who lives in Jinan, the capital of China’s Shandong province, is one of the oldest living voices of dissent in China. On Aug. 1, he was speaking by telephone to a live broadcast in Mandarin with the Voice of America when he informed the anchor that police had just broken into his home and demanded he stop. He refused. “I am entitled to express my opinion. This is my freedom of speech,” he declared. Then the line went dead. VOA said it was unable to reach him again.

Mr. Wenguang, now in his 80s, who once taught physics and economics, has been speaking out against China’s Communist Party for more than 50 years and has suffered prison time, beatings and harassment. The latest attempt to silence him is another chapter in one man’s long struggle — but it also reflects a campaign to pressure scholars and intellectuals to fall in line behind the party and President Xi Jinping, China’s strongman who has shown little tolerance for dissent while building a cult of personality not seen in China since Mao Zedong. Under Mr. Xi, ideological campaigns have returned, targeting such ideas as freedom of speech and assembly. China is also engaging in campaigns to spread its ideology and influence far beyond its borders.

A new campaign aims at intellectuals. The party has announced it will seek to wage “unremitting struggle” among them by organizing study sessions about party ideology to make them more “patriotic.” Radio Free Asia, which published an account of the new drive, quoted a former official in the propaganda department as saying it was essentially an order to attempt mass brainwashing. If all this language sounds archaic, it is — harking back to Mao and the harsh years before the opening and reforms of the past four decades. Mr. Xi has attempted to extinguish freedom of thought wherever it might threaten him or the party’s monopoly on power. He told news media organizations in 2016 they should “have the party as their family name.” Now, he is sending a similar message to scholars that they must obey. Universities have been in Mr. Xi’s crosshairs for tighter control.

It was recently demonstrated yet again how one freethinking voice can have a wide impact. On July 24, Xu Zhangrun, a professor of law at Tsinghua University in Beijing, published a lengthy essay that boldly questioned China’s current direction and specifically criticized Mr. Xi and his throwback to Maoism. Mr. Xu said “an emergency brake must be applied to the personality cult” of the Chinese president and expressed fear that China is returning to totalitarianism. The essay offers an example of how unfettered thinking in the open is valuable to a society and to its leaders. Mr. Xu calls on China not to throw away the gains of the era of reform and opening. His advice would benefit China far more than the dreary stuff about loyalty and obedience pounded out in the party’s study sessions.