BEIJING — Inside a bustling, 700-person newsroom in downtown Beijing, Hu Xijin leads a 24-hour propaganda machine that some media scholars call China’s Fox News.

Mr. Hu was one of the first to defend China’s vast detention of Muslims against international criticism. His newspaper has described Secretary of State Mike Pompeo as crazy. Thirty years ago, he marched with students on Tiananmen Square demanding democracy in China, but now he is a leading critic of protesters in Hong Kong who have been resisting Chinese rule.

China is rife with nationalist voices. But Mr. Hu stands out because of his position as the top editor of The Global Times, a popular tabloid controlled by the ruling Communist Party, and his flair for verbal warfare against the United States and the Trump administration. To Mr. Hu, virtually every criticism of China is an opportunity to launch a counterattack about what he derides as the hypocrisy of Beijing’s critics.

As the trade war between China and the United States has escalated, Mr. Hu has played a critical role in the party’s mission to tell the world that China will not back down. He was once dismissed by many as a commentator whose self-satisfied broadsides did not always reflect China’s official views. But Mr. Hu is now increasingly seen as a combative public voice of the administration of President Xi Jinping in an era of more open rivalry with the United States.