Donald Trump doesn’t become the proper focus of Enemies: The President, Justice & the FBI until its fourth and final episode. Yet in every respect, our current commander-in-chief is the sole reason for the existence of Alex Gibney’s Showtime documentary series, which details the often contentious modern relationship between the FBI and the president—and, in doing so, argues that nothing is more vitally important for our democracy than the independence of its law-enforcement services.

That closing episode, dubbed “You’re Fired,” won’t air until December 9, and considering Trump’s penchant for radically altering the geopolitical landscape with a few vomitous tweets, the version provided to press is only a temporary one, apt to be altered by forthcoming events. Nonetheless, both it and its three preceding installments—based on Tim Weiner’s book Enemies: A History of the FBI, and led by Weiner’s on-camera interviews—operate as commentaries, both direct and indirect, on Trump. More specifically, they’re rooted in Trump’s antagonistic rapport with former FBI Director James Comey, whom the president famously fired on May 9, 2017, thus begetting cries of “obstruction of justice!” from opponents—since Comey was overseeing an investigation into the president’s possible collusion with Russia during the 2016 election—and compelling Comey to testify about his boss’ requests for “loyalty” and general bullying, intimidating manner, which the FBI bigwig documented in thorough notes.

“You’re Fired” is indisputably Enemies’ centerpiece (it runs 97 minutes, versus the other three hour-long episodes). And while it unfortunately doesn’t feature the participation of Comey himself, Gibney—who directed this chapter, and produced the series—shrewdly uses Comey’s audiobook recording as narration. That lends the action a biographical, insider-y feel, and better still, Gibney doesn’t just begin this particular tale in 2016. Instead, he first dials the clock back to George W. Bush’s administration. It was then that Comey was hired as assistant attorney general working under AG John Ashcroft and alongside FBI Director Robert Mueller, and it was during that period that he first established himself as an upstanding and dedicated law-enforcement official.

As Gibney depicts with the sort of pulse-pounding suspense that marks his best documentary output, Comey found himself in a showdown with Bush and Dick Cheney over Stellar Wind, a covert piece of post-9/11 legislation that gave the president vast (and, to many legal minds, illegal) power to spy on the American public. When it came up for one of its periodic renewals, Comey—thrust into the role of attorney general due to John Ashcroft’s debilitating illness—refused to re-up Stellar Wind, which didn’t sit well with the administration. Thus a literal standoff was born, with Comey racing to Ashcroft’s hospital bed to stop Bush’s Chief of Staff Andrew Card and White House Counsel Alberto Gonzales from getting the incapacitated Ashcroft to sign off on the law behind Comey’s back, and later testifying in a 2007 Senate Judiciary Committee hearing about his behavior.

It’s a thrilling story, and one that makes clear Comey’s staunch principles and capacity to back them up with action—including threatening to resign, which, when coupled with similar commitments from Mueller and other colleagues, convinced the Bush team to stand down on the measure. It also proves Comey’s fondness for public-speaking transparency, which has led many to see him as something of a grandstander. Most crucially, though, it demonstrates a lesson proffered by all four episodes of Enemies—namely, that for the good of American democracy, the FBI must work not as an extension of the executive branch, but as an institution that holds everyone accountable for wrongdoing, the president included.

That definitely applies to Enemies’ portrait of Trump and Comey, given that Trump has demolished standards by firing his FBI chief explicitly because he didn’t like being investigated for potentially treasonous conduct. And it’s also relevant in the show’s first three passages, which concern, respectively, Richard Nixon and Watergate, Ronald Reagan and Iran-Contra, and Bill Clinton and Troopergate, Travelgate, Whitewater, and Monicagate (to name a few). Premiering in chronological order, and directed by Jed Rothstein, they reveal how the FBI’s relationship with the president transformed from being intimate during J. Edgar Hoover’s reign, to adversarial after his departure, beginning with Watergate, and then again with Iran-Contra and Bill Clinton’s numerous scandals, when the FBI treated the president as a figure who—under the right circumstances—could be a legitimate criminal suspect.

Enemies contends throughout that the FBI should remain free to do its business, even if that means looking into the commander-in-chief. Not that maintaining such sovereignty is an assurance of success, as was made plain by the Iran-Contra fiasco, during which President Reagan undoubtedly broke the law, and yet got away with it, thanks to the fact that, unlike during Watergate, none of his closest advisers and co-conspirators chose to turn on him to save their own skin. In its rundown of Nixon, Reagan and Clinton’s run-ins with the FBI, all bolstered by succinct use of archival material and new interviews with relevant big-time players, Enemies illustrates that presidents are preternaturally drawn to overstepping their boundaries, potential consequences be damned. And more dispiriting still, it forwards the idea that the FBI isn’t always able to rein in a president eager to do whatever it takes to achieve his ends.

It’s easy to see how those past stories relate to our present national circumstances, and Enemies doesn’t ever let one forget that its real object of disaffection is Donald Trump. During his recaps of Nixon, Reagan and Clinton, Rothstein repeatedly cuts to our orange-faced leader in order to highlight how the past is constantly repeated, and also how previous presidents helped set precedents—both big and small—for our current national nightmare. Not that the showrunners are pinning the blame for Trump’s reign of chaos on his Oval Office ancestors; on the contrary, Rothstein, Gibney and Weiner convincingly illustrate how Trump has decimated prior paradigms by firing Comey. But in their gripping and informative four-part series, they suggest that he’s merely the most extreme example of a president pitting himself directly against the FBI—and how the winner of that conflict is, unfortunately, anything but guaranteed.