The past month has seen talk of “constitutional crisis” on both sides of the Atlantic. In the United States, President Trump’s use of a national emergency to fund his proposed border wall led 12 Senate Republicans, wary of creating a precedent for executive overreach, to join with Democrats on a bill to block his executive order. After Trump vetoed the bill, Speaker Nancy Pelosi declared, “The president has decided to be in defiance of the Constitution, to deface it with his actions.”

Across the Atlantic, the United Kingdom’s constitutional crisis hinges on Prime Minister Theresa May’s determination to take the country out of the European Union. Although May’s government and the E.U. have agreed to a deal on the terms of Britain’s departure, which had been scheduled for this Friday, the prime minister has thus far failed to secure necessary parliamentary approval for the agreement, losing two votes on the deal by historic margins. Last week, it looked as if she might finally have had the votes — but then Speaker of the House of Commons John Bercow invoked a precedent dating back to 1604 and refused to allow a third vote. His assertion of parliamentary sovereignty in the face of executive prerogative has provoked a constitutional crisis in Britain, a country where the balance of power has historically rested firmly with the executive.

The emergence of an empowered executive in the United States and a defensive one in the United Kingdom signals a remarkable reversal of historical roles. Traditionally, the prime minister, chosen for her ability to command a parliamentary majority, towers over the legislative branch. The U.S. system was explicitly designed to be the reverse: The founders drafted the Constitution to ensure that the president would not wield the unchecked power of the British executive. And yet we are now in the paradoxical position where the U.S. president seems, for the moment, to have outmaneuvered Congress, while the British speaker has put the prime minister in temporary check.

How did this flip occur? The power of the presidency has been growing for the better part of a century. But on the British side, the roots of the current crisis trace to the start of the 17th century. The precedent that Bercow cited to justify his move dates to the reign of King James I. Parliament had grown frustrated by the monarch’s attempts to bully the legislature by repeatedly bringing measures up for reconsideration. As a result, Parliament pronounced on April 4, 1604: “That a question being once made, and carried in the affirmative or negative, cannot be questioned again, but must stand as a judgement of the House.”

Over the past four centuries, the precedent has been used not only to curb executive power, but also to foreclose debate on exceptionally divisive issues, as when Speaker James Lowther determined in May 1912 that the House could not consider another bill on women’s suffrage, having already rejected a voting bill that March by a margin of 14.

Many have accused Bercow of wielding the precedent for political reasons because it is well known that he personally opposes Brexit (although as speaker, he is meant to be impartial). This is not the first time in the past months that he has used his position to impede May’s Brexit agenda. Yet, his Brexit views notwithstanding, he is also widely known as a defender of the rights of MPs. As he said on Thursday, “I believe passionately in the institution of Parliament, of the rights of members of this House and their commitment to their duty.” In refusing to work with MPs to find an alternative and instead continually forcing them to vote on her deal, Bercow argued, May was infringing on those rights and undermining that duty.

The speaker’s announcement temporarily put the prime minister in check. Unable to bring her bill up for a vote last week, she had no choice but to go to Brussels and beg the European Union to give her more time. But then, in an unprecedented step, the prime minister pulled a page from the U.S. presidential playbook: She made a direct televised address to the British public, proclaiming to them that “I am on your side” in the face of parliamentary determination to thwart the will of the public by not allowing her deal to be voted through. The address was a rebuke of Bercow and of those in her own coalition and in the opposition who had not come on board with her plan. It was also a remarkable effort by the British executive to harness the power of public opinion to break parliamentary opposition.

Such a move no doubt sounds unremarkable to Americans. Over the course of the 20th century, such appeals have become a prominent strategy in U.S. presidential politics. Franklin Roosevelt regularly went on radio to ask the American people for their support for his experimental programs. Lyndon B. Johnson and Richard M. Nixon regularly appeared on television to rally support for their Vietnam policies. Donald Trump most recently resorted to such a tactic on Jan. 8, when he addressed the American people about the need for a border wall to confront the “national crisis” at the Mexican border.

In Britain, however, such things are just not done. Constitutionally, the prime minister holds more power than the U.S. president, but that power is vested in her position as the leader of a parliamentary majority, not in a direct mandate from the British public. In normal times, that distinction makes the idea of appealing to public opinion to put pressure on MPs unnecessary and unseemly.

But Brexit is not normal times, and May has stronger support from the public than she does from Parliament. On Monday, she took a gamble that that public support could be harnessed to force the speaker to back down and secure her a victory in a third parliamentary vote on her Brexit plan.

There are signs that the move, denounced by many in Britain as Trumpian demagoguery, may have badly misfired. But if her gambit succeeds, May’s Goliath will have effectively wielded the shield of public opinion to protect herself from Bercow’s procedural slingshot. In the process, she will have recaptured the power of the executive against the legislature, restoring the traditional relationship between the two bodies with new and, for many Britons, unsettling tactics.