When the Framers wrote impeachment into the Constitution, they were drawing on a long history of English common law. But situated within that history, the first impeachment of a head of state had taken place relatively recently—less than 150 years before the drafting of the Constitution. On January 1, 1649, the House of Commons impeached Charles Stuart, then King Charles I of England, for attempting “to subvert the fundamental Laws and Liberties of this Nation.”

The circumstances that led Parliament to break this new ground were undoubtedly extreme. For most of the prior decade, England had been wracked by civil war triggered by Charles I’s quest to consolidate royal power away from Parliament. Parliament asserted its independent political legitimacy. And by 1642, both sides had formed their own armies, with parliamentary forces led in part by England’s soon-to-be military dictator, Oliver Cromwell. Parliamentary forces captured and then detained Charles on the Isle of Wight at the end of 1648. By this point, estimates are that as many as 100,000 were left dead from the conflict.

With Charles in custody, Parliament confronted the difficult question of what to do with him. After months of negotiation, the House of Commons decided to impeach him for “high and Treasonable offenses” and, over the House of Lords’s objections, remit him for an impeachment trial before the newly created High Court of Justice. Within a month, Charles was convicted by the court and then removed from office in a very 17th century way: beheading.

Other than antiquarian interest, this first removal of a head of state from office via impeachment offers three practical takeaways for those members of Congress currently weighing the impeachment of President Trump: one foundational lesson on why impeachment is more than just politics, one procedural lesson on the role of executive privilege in impeachment proceedings and one substantive lesson on what offenses are impeachable in the first place.

The foundational lesson helps to answer the question confronting legislators today: Why impeachment? If the president is due to face a reelection battle in less than a year, why bother with impeachment? Why not just trust the political process to remove a bad head of state from office?

In 1648, Parliament also reckoned with the question of whether to merely resort to politics. The obvious political solution in the 17th century, though, was assassination. Whereas political will is now communicated with a ballot, 17th century political frustration was more often expressed with a sword. History offered plenty of examples for removing the head of state this way. And some in Parliament openly advocated poisoning Charles to be done with him. But Parliament chose instead the legalistic mechanism of impeachment.

Parliament had impeached many lesser royal functionaries before, including one of Charles’s closest advisers. But impeaching the king for “high and Treasonable offenses” seemed—not without reason—to violate the basic framework of English monarchical government, under which the person of the king embodied the state and the king could “do no wrong.” In impeaching Charles, though, Parliament sought to clarify the terms of England’s unwritten constitution in ways that profoundly shaped America’s Founding generation and its understanding of what a head of state was. (In 1775, Benjamin Franklin even penned an epitaph celebrating the judge who presided over Charles’s trial, a man who died of natural causes only to have his corpse exhumed and posthumously executed for treason after Charles I’s son took back the throne in 1660.)

In choosing to impeach, Parliament sought to repudiate as a matter of law the l’état c’est moi notion that the office of the king and the person of the king were indivisible. The articles of impeachment levied against Charles at his trial began from the premise that he was like any other noble official under the law, “trusted with a limited Power to govern by, and according to the Laws of the Land, and not otherwise, and by his Trust, Oath and Office, being obliged to use the Power committed to him for the Good and Benefit of the People.” As king, in other words, he could only act for the public and under the law. By betraying his oath and violating the “Laws of the Land,” he forfeited his claim to act as the king at all.

It was not, therefore, Charles I, king of England, who was impeached and beheaded. It was Charles Stuart, the man, who had “carried on for the advancement and upholding of a personal interest of Will, Power, and pretended Prerogative to himself and his family, against the public interest, common right, liberty, justice, and peace of the people of this Nation.” In acting against the law, he acted for himself. And by impeaching him and putting him on trial, Parliament sought to prove that Charles Stuart, the man, could not be trusted to act as king.

The facts surrounding the allegation that President Trump sought Ukrainian assistance for his 2020 presidential campaign are still coming to light. But one passage from the now-released whistleblower complaint seems to ring across the centuries. In recounting the now-public telephone conversation between President Trump and Ukrainian President Volodymyr Zelensky, the whistleblower writes that some participants on the call reported that they “witnessed the President abuse his office for personal gain.”

It was not, in other words, President Trump speaking to Ukrainian President Zelensky. It was Donald Trump. And the impeachment question now before Congress asks whether Donald Trump can still be trusted to act as president.

The second lesson is procedural. As soon as the Ukraine allegations surfaced, the president’s defenders invoked “executive privilege.” The Office of Legal Counsel’s principal reason for withholding the whistleblower complaint from the House Intelligence Committee was that executive privilege attaches to the president’s diplomatic communications, thus a complaint about the president’s call with a foreign leader was off-limits to Congress. And while both the complaint and the readout of the phone call were ultimately released, executive privilege will undoubtedly be invoked again as any impeachment inquiry moves forward.

The impeachment of Charles Stuart, however, suggests that a head of state’s communications enjoy no privilege when they contain evidence of impeachable conduct. Executive privilege is a species of sovereign immunity. And during his trial, Charles based his whole defense on his assertion of sovereign immunity, insisting that no “impeachment can lie against the King, they all going in his name.” But Charles’s claim of sovereign immunity was rejected because the very purpose of impeachment is to determine whether the officeholder has betrayed the office that enjoys the immunity. Heads of state are impeached, in other words, in what we would now call their “personal capacity,” not as sovereigns.

Whatever privilege Charles may have had to withhold his correspondence as king, therefore, offered no protection once the question was whether he had committed impeachable conduct. The final witness called at Charles’s trial was his former scrivener, who testified about the content of the king’s diplomatic correspondence. And the prosecution’s closing pieces of evidence, as recounted in “State Trials”, were “[s]everal Papers and Letters of the King’s, under his own hand, and of his own writing, and other papers,” which were “produced and read in open court.”

The impeachment of Charles Stuart therefore belies any claim that Donald Trump, or any other occupant of the presidency, can use the presidency’s privileges to conceal evidence of their own impeachable conduct. If, as is alleged, President Trump sought to procure the assistance of a foreign power for his own personal, partisan ends, the impeachment of Charles Stuart offers strong historical support for the conclusion that any communications seeking to achieve those ends enjoy no privilege against being produced in impeachment proceedings.

The last lesson from Charles’s impeachment helps those in Congress answer the substantive question of whether President Trump’s alleged abuse of his diplomatic powers is, in fact, impeachable. The vague tautology that all abuses of power constitute “high Crimes and Misdemeanors” both proves too much and too little. Scholars have dug up seemingly germane quotes from the Founders, such as Madison’s injunction that impeachment is necessary because the president might “pervert his administration into a scheme of peculation or oppression. He might betray his trust to foreign powers.” But actual precedents are—thankfully—hard to come by. There are no examples of a president being impeached for abusing his diplomatic powers.

Taking advantage of this vacuum, President Trump and his supporters have insisted that any exercise of discretionary presidential power is neither criminal nor impeachable. And while not going quite that far, John Yoo has already taken to the op-ed pages of the New York Times to argue that impeaching a president for abusing his foreign relations powers is a near impossibility, in no small part because of executive privilege.

The impeachment of Charles Stuart, however, suggests that Yoo has it precisely backward. During the Constitutional Convention debates over the Impeachment Clause, Benjamin Franklin cited the impeachment of Charles Stuart as one of the principal reasons the impeachment process needed to be formalized in the Constitution. And Gouverneur Morris supported the idea, arguing that Congress needed the power to impeach a president for “treachery” and “corrupting his electors.”

Parliament, for its part, also described Charles’s acts as treasonous, though this characterization was by no means obvious in a literal sense at the time. The English law of treason was largely defined as crimes committed against the person of the king. But as Geoffrey Robertson recounts in “The Tyrannicide Brief”, Charles Stuart became a traitor to his office as king and to England from the moment he sought to unlawfully subvert the proper functioning of English democracy. And what made his conduct all the more “treasonous” was the fact that he had sought to do it with assistance from abroad.

The final charge against Charles was for the “prosecution of his said evil designs, He, the said Charles Stuart, doth still continue his commissions to the said Prince, and other Rebels and Revolters both English and Foreigners.” The “Prince” was the future Charles II, who spent most of the English Civil War abroad acting as his father’s envoy, agitating the governments of his cousin—Louis XIV of France—and his sister—Princess Mary of the Netherlands—to come to his father’s aid against Parliament. Also among the “Foreigners” were the Irish, whom Charles had encouraged to join his cause in exchange for more favorable treatment once he had consolidated power. This charge against Charles, stated more simply, was that he sought to “procure” assistance from abroad in his efforts to attack his domestic political rivals and to subvert English democracy. This betrayed his “Trust, Oath and Office” as the defender of the English people.

President Trump’s alleged efforts to enlist the government of Ukraine against his domestic political rivals implicates the same civic evil. As Parliament accused Charles Stuart of doing, President Trump is alleged to have used his position as head of state to “procure” the assistance of “Foreigners” for his “personal interest of Will, Power, and pretended Prerogative” and “against the public interest.” And if true, he would have done this in violation of his oath to faithfully execute the laws of the United States, in particular those laws whose very purpose is to protect the proper functioning of America’s electoral democracy.

If the allegations against him are true, President Trump has not simply abused the powers of his office. Like Charles Stuart, he has subverted his office’s very purpose for personal gain.

To be sure, the analogy between President Trump and Charles Stuart should not be overstated. President Trump has not yet raised his own army and persisted in a brutal civil war that has left the equivalent of six million Americans dead. And his alleged conduct also does not appear to meet the literal constitutional definition given to the crime of “Treason.” But in kind if not in scale, President Trump’s alleged abuses of the foreign relations power entail the same betrayal of the head of state’s oath of office, the same elevation of self over service, and the same collusion with foreign powers to gain an unlawful partisan advantage against domestic political rivals that led Parliament to impeach Charles Stuart. The first impeachment of a head of state therefore offers a precedent for impeaching a president alleged to have abused his diplomatic powers in a way that failed, to borrow a phrase, to put America first.