When Edward Snowden first came forward in 2013 as the leaker of the biggest trove of National Security Agency secrets ever spilled, he ended his first interview by noting that his greatest concern was about the agency’s future. He feared that a less scrupulous commander-in-chief would take charge of the executive branch and with it, the most highly resourced surveillance agency in the world, ready to be exploited in new and troubling ways. “There will be nothing the people can do at that point to oppose it,” Snowden warned. “And it will be turnkey tyranny.”

Three years later, America has watched Donald Trump praise foreign dictators from Kim Jong Un to Vladimir Putin, vow to appoint a special prosecutor to investigate his opponent, Hillary Clinton, if he’s elected, and call for Russian hackers to dig up Clinton’s emails. “I wish I had that power,” he later said in a campaign speech. “Man, that would be power.” If that statement didn’t sufficiently reveal Trump’s lust for surveillance capabilities, he reportedly listened in on phone calls between staff and guests at his Mar-a-Lago resort in Palm Beach in the mid-2000s. As Trump and Clinton prepare for their final debate tonight—this time focused on national security—NSA alumni as well as critics are concerned that Trump may be exactly the turnkey tyrant Snowden had in mind.

“This is someone who displays a kind of personal vindictiveness that makes Nixon look Christlike,” says Julian Sanchez, a privacy-focused research fellow for the Cato Institute. “There’s every reason to be worried about those instincts and how they’d lead him to attempt to abuse this surveillance power.”

To be sure, Trump appears to have a very slim chance of winning November’s election. But setting aside lopsided poll numbers and imagining what a President Trump might do with the NSA raises the broader question of how tyrant-proof the agency really is: whether its vast surveillance powers are held in check by law or simply by the discretion of the people who control it. Even the NSA’s legal defenders, like former NSA counsel Susan Hennessey, say the agency’s regulations don’t entirely protect it from a president who’s dead set on abusing its capabilities. “No one should kid themselves about the idea that in the wrong hands, it couldn’t do quite a bit that’s very scary,” she says.

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