Hong Kong is teetering on a knife’s edge. Weeks of massive pro-democracy protests have been met with increasingly harsh official rhetoric. Chinese authorities have publicized the buildup an armored military police force just across the border. Some fear another Tiananmen massacre.

No one wants it, but that doesn’t mean it won’t happen.

Policing the protests is in the hands of Hong Kong authorities, but it’s the mainland government that will ultimately decide whether to crack down. If the experience of 30 years ago is an indication — and it probably is — China is willing to use force, and take a big hit to its international standing, if it deems the protest a threat to the Communist Party and the system. But the cost would be substantial at a time when China can ill afford it. Authorities will try to avoid that. 

On the protesters’ side, a largely leaderless movement capable of bringing hundreds of thousands of people onto the streets will have to curtail periodic outbreaks of violence. If it manages to win concessions, it will somehow have to know when to stop – and after the spotlight is off, it will need to protect itself from slowly being dismantled by police and the courts.

There is a difference between a protest like that in Tiananmen Square in the heart of the capital and one in an outlying metropolis with its own administration and unique legal status. The agreement returning Hong Kong to Chinese sovereignty was workable over the long term only with a heavy dose of luck, a fair amount of wishful thinking and a willingness to sometimes look the other way. 

These protests, which started over an extradition agreement with the Chinese mainland, go to the heart of that compromise. Like other waves of discontent since the handover in 1997, the tension is between China’s drive to incorporate Hong Kong and the desire of many of its residents to maintain established freedoms.

A huge, peaceful protest on Sunday showed the pro-democracy movement could pull back from the more confrontational tactics that included occupation of Hong Kong’s airport, which led to the cancelation of hundreds of flights, and clashes with police using tear gas and rubber bullets. 

Protesters have adopted a slogan from Bruce Lee – “be water” — to guide them. A decentralized movement has no real leaders who can be arrested to stop it. Pro-democracy legislators who have tried to get between demonstrators and police say neither side welcomes them. Hong Kong’s administration has suspended, but not withdrawn, the offending extradition legislation. If it’s withdrawn, will the wisdom of the crowd conclude that’s good enough? 

Then, provided that Hong Kong is lucky enough to end this peacefully, how do protesters protect themselves from slow, steady payback? It took five years, but the final chapter of the last mass protests was written only four month ago, when its leaders were sentenced to jail. 

Chinese officials know how to play a long game. Their first challenge, though, is simply understanding what’s going on. This story by reporters for Hong Kong’s South China Morning Post illustrates just how much information – and how little understanding – they have had. It can be hard for a Communist Party apparatchik to grasp why prosperous, law-abiding Hong Kong residents would protest over an extradition bill. 

Perhaps officials find a way to make a concession they can live with. For now, though, they’re squeezing businesses in the lucrative Hong Kong market to take the government’s side. They’ve declared that the protests border on terrorism, and warn darkly of foreign interference. Across Hong Kong’s border, Chinese police with body armor, helmets and shields have held a series of well-publicized and not-very-subtle anti-riot drills. 

The big danger is that Hong Kong will inspire unrest on the mainland, just at a point when China’s economy is slowing – the result of structural changes and President Trump’s trade war. Mainland protests could threaten the legitimacy of the Communist Party and the whole political system. 

Trump finally spoke out Sunday against a crackdown, but his overall response has been muddled. Going easy on China’s approach to Hong Kong in a bid to make a trade deal more likely might be self-defeating. In 1989, Chinese officials looked at the unfolding disintegration of the Soviet Union and decided they would rather weather international condemnation of the Tiananmen crackdown. Three decades later, the size of their economy ensures China can’t simply be isolated or ignored. But a harder view of China is taking shape across the U.S. political spectrum, and while Beijing is courting European countries, it would be impossible to continue business as usual. Plus, putting a violent end to the protests would send a horrible message to Taiwan, where China hopes one day to apply a version of the Hong Kong “one country, two systems” model.

Major street violent or protests that make Hong Kong unmanageable could provoke China to crush the demonstrations. More likely, though, is a continuation of sharp rhetoric seeking to dive Hong Kong residents and dissuading mainlanders from joining them. Add to that the application of quiet pressure via jail time, lost jobs or other penalties that ensure protesters and those who support them pay a price. It might be enough.