Once, on a visit to China in August 2015, I heard an odd theory about one of the most powerful men in the world. Xi Jinping, the president of China, would prefer to travel overseas more, but he dreaded doing so, according to the theory. Why? Because he feared deplaning in Beijing and seeing the other six members of the Politburo Standing Committee, China’s top ruling body, lined up to meet him. “Thank you for your service,” each man would say solemnly, shaking Xi’s hand and looking him in the eye. Then, in this nightmarish scenario, military police would arrest him, and he would spend the rest of his life under house arrest.

It’s impossible to confirm such a story. And yet it illustrates how little the outside world actually knows about both what goes on at the top of the Party and how firmly Xi is in charge. Xi, who took power in November 2012, has long been viewed as China’s most powerful leader in decades—at least since Deng Xiaoping, who ruled China from the late 1970s until the 1990s; and perhaps since Mao Zedong, who reshaped China in ways both positive and devastating during his 1949-1976 reign. And yet, regarding Xi’s relationship with China’s top elite and his relations with the military—arguably the two most important indicators of his power—the world remains in the dark. That the world knows so little about how other top leaders check Xi’s power does not mean he soars above them.

When Xi meets with President Donald Trump Thursday and Friday in Florida, expect a flurry of stories predicated on the assumption that Xi is fully in charge of the three levers of Chinese power: the Chinese Community Party, of which he is party secretary; the Chinese state, which he presides over; and the Central Military Commission (CMC), which he chairs. To be clear, it’s certainly possible, even likely, that Xi dominates all three. But doing so requires a complicated dance, beyond the view of outsiders, between him and retired leaders, regional party secretaries, princelings, CEOs, generals, top aides, and, most crucially, the Standing Committee. The various steps these men take has a great impact on Sino-U.S. relations, and on the upcoming summit. How much leeway does Xi have to make on-the-spot decisions, particularly those involving China’s support for North Korea, or the militarization of the South China Sea? Can he compromise on trade? Does he have institutional support to change China’s future? The answer to at least one of those questions may well be no, meaning that Trump will be negotiating with someone without a solid grip on the reins of power, in thrall to the top of the party.

Why is the top of the CCP so opaque? Aside from its Leninist roots, the simplest answer is that the party believes projecting a united front is crucial. Just how opaque is it? In July 2016, The Wall Street Journal published an article titled “Discord Between China’s Top Two Leaders Spills Into the Open.” Their main evidence for that assertion: conflicting messages Xi and China’s number two official, Premier Li Keqiang, delivered about reforming China’s state-owned sector in a private meeting. Subtle stuff indeed.

It also doesn’t help that the Standing Committee members, Xi included, rarely give interviews to Western media. When they do, they tend to offer either milquetoast remarks to sympathetic interlocutors, or send in tepid written responses.

In that way, Xi and Trump are opposites. Trump has lived in the public eye for the last three decades: The world is well aware of his personal weaknesses, the flaws in his leadership style, and, now, the contempt many in the U.S. government and bureaucracy feel for his ideas. Xi is a product of the Party, one of the world’s most secretive large organizations—and one which requires officials to be publicly modest and low key. In a 2000 interview with the magazine China Profiles, when Xi was a party official in the southern Chinese province of Fujian, he said he had rejected more than 100 interview requests. “People’s abilities are limited,” he said, explaining why top Chinese officials should eschew publicity. “If you leave the broad masses of the people, if you leave collective leadership, you will be a total failure.”

The extent to which Xi subscribes to those views today is unknown. Those who have met him often describe him as confident, charming, and comfortable speaking to foreign delegations without notes. But without further data, it is imprudent to assume he is firmly in control. In other words, just because we don’t see something, doesn’t mean it’s not happening. (Besides, it’s very unlikely these conversations touch upon the sensitivities of Xi’s relations with the top elite. Not long ago, I met an American who occasionally dines with a current member of the Standing Committee. What did that member think about Xi’s anti-corruption campaign? “I never ask him,” the American told me. “If I did, I wouldn’t be invited back to dinner.”)

There is no way of really knowing whether the other six members of the Standing Committee want Xi as chairman, or whether they’d prefer someone like Li in charge. How do they feel about Xi’s leadership style? The direction he’s taking China? Preserving a united front allows the committee to preserve its veil of secrecy.

Perhaps the most significant and opaque criterion for assessing Xi’s power is his relationship with the top of the PLA. (China does not have a national army. Rather, the party has an army: The PLA swears fealty to the Party, and not to the government, nor the nation.) Xi seems to be firmly in charge of the military. Since taking office, he has cut the size of the ground force, instituted a new command and control structure, and, as part of a nation-wide anti-corruption campaign, purged officials at all ranks. In a surprising move, he purged the two men who served as his predecessor’s CMC vice-chairmen, Xu Caihou and Guo Boxiong, for alleged corruption. And the crackdown in the military isn’t over: In December, China’s ministry of defense announced a corruption probe into General Wang Jianping, the CMC’s deputy chief of the joint staff department and the highest-ranking active-duty officer Xi has targeted.

And yet, how closely the top of the army actually listens to Xi, and how much its upper echelon resents him for his corruption purges is unknown. “For the most part,” Xi didn’t pick the top PLA officials—but was stuck with [those] already at the highest levels, Philip Saunders, director of the Center for the Study of Chinese Military Affairs at the National Defense University, told me. Do Xu and Guo’s replacements as vice-chairman respect Xi and his decisions? It’s unclear. “One big unanswered question is who he listens to and who he trusts at the top.”

In his September 2015 visit to Washington, Xi infamously said “China does not intend to pursue militarization” of the Spratlys, a disputed island chain in the South China Sea. And yet, 22 months later, China has militarized some of the islands to the extent that it now appears able to deploy warplanes from them, and the South China Sea is now one of the biggest points of tension in Sino-U.S. relations. Did Xi make a pledge and then change his mind? Did he intentionally lie? Or did the PLA force his hand, making him do something he did not want to do?

On the one hand, while Xi—a seasoned politician with a large staff who have likely been preparing for this meeting for months—is much better prepared for this week’s summit than Trump, he may also be more constrained than the White House expects, both in terms of what he can push and what he can offer. This could reduce the odds that Xi will run circles around Trump, an outcome some experts are predicting. But Xi may be less able to follow through on deals than the Trump administration expects. Does he have the domestic support to follow through on Trump’s (misguided) request to lower the trade deficit between the two countries? Could he permit China’s currency the RMB trade in a larger band, allowing Trump to proclaim Beijing has taken steps to end the manipulation of its currency? Besides the PR value, what good is announcing a deal on, say, curtailing North Korea’s weapons program if Xi can’t enforce it?

In any event: Trump is about to gain considerable insight into how Xi thinks, and what he’s capable of.