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– The Shenzhen Bay Sports Center rises along the shore with the green hills of Hong Kong visible across the water. It normally bustles with a variety of youth sports programs and dance, art and language academies, including one that advertises a “Hong Kong Style Education.”

In recent days, it has become a staging ground for olive-green military transports and armored personnel carriers that arrived Aug. 11. By massing the troops within view of Hong Kong, the semiautonomous territory convulsed by protests, China is delivering a strong warning that the use of force remains an option for Beijing. It is also a stark reminder that military power remains the bedrock of the party’s legitimacy.

“It’s a credible threat,” said Minxin Pei, a professor at Claremont McKenna College in California. “The Chinese government does not want to leave any doubt that, if necessary, it will act.”

China’s leader, Xi Jinping, has governed with an increasingly iron fist. The deployment does not appear to be the prelude to a military intervention in Hong Kong, but few analysts expressed doubt that China would act if Xi believed the country’s sovereignty over the territory was jeopardized.

“How can he regard the Hong Kong movement as a pure democratic movement?” said Tian Feilong, executive director of a research institute on Hong Kong policy in Beijing. Xi is likely to perceive the protests not just as a call for democracy in Hong Kong, but also as an effort to topple the Communist Party, he said. “He is very politically alert.”

Xi’s government, he said, has most likely completed preparations for an intervention but is holding off as long as the local authorities manage to keep the protests contained. That calculus could change, he and other analysts said, if the protests succeed in crippling the government or other institutions, such as the courts, which will soon begin hearing the first cases of those arrested in the demonstrations. In what some observers see as a worrying sign, officials in Beijing have called the protesters’ actions “close to terrorism.”

The use of force, however, would be fraught with risks for Xi, who is juggling economic headwinds and deteriorating relations with the U.S. under President Donald Trump.

The country and the party are still haunted by the use of the army to crush the Tiananmen Square protest movement 30 years ago this summer, which resulted in international isolation and sanctions. A military crackdown could spell the end of Hong Kong’s role as an international financial center and the political formula under which Beijing grants the territory freedoms unseen on the mainland.

“The military solution would have many urgent and disruptive effects,” said Wu Qiang, a political analyst in Beijing. “It would be political suicide for the Communist Party of China and the ‘one country, two systems’ arrangement of Hong Kong.”

More nationalistic voices have brushed aside such fretting, noting that China is a much stronger and diplomatically confident nation than the one that endured international condemnation after the Tiananmen crackdown.

The deployment in Shenzhen was clearly meant to focus attention in Hong Kong and beyond. A white bridge that connects Shenzhen to Hong Kong is 2 miles away.

The message was amplified by no less than Trump, who disclosed on Twitter that U.S. intelligence agencies had spotted the Chinese troops massing at the border. “Everyone should be calm and safe!”

It remains to be seen how effective Beijing’s posturing will be. The authorities have from the start misjudged the depth of the anger driving people into the streets. While the deployment and increasingly blunt warnings from officials have rattled nerves, they seem to have had little effect on those who view the struggle as one crucial for preserving Hong Kong’s freedoms.

The growing threats of military action came as violent clashes have escalated. Public anger on the mainland spiked last week when protesters at Hong Kong International Airport tied up and beat two men from China.

The Hong Kong garrison of the People’s Liberation Army is based in what was formerly the British military headquarters. The garrison includes 19 sites around the territory, but many of its soldiers — estimates vary from 6,000 to 10,000 — live and train in bases across the border in Shenzhen.

The deployment of the People’s Armed Police, though, shows Beijing has options other than the army. The armed police force has a mission of maintaining internal security on the mainland, including responding to terrorist attacks, riots and rebellions.