Forbidden or not, this is certainly new territory. Britain’s Supreme Court is only 10 years old, and until Brexit came along, its rulings were not usually the subject of such intense scrutiny. That changed in January 2017, when it declared that former Prime Minister Theresa May could not pull Britain out of the EU without a vote in Parliament. After a lower court had come to the same conclusion, the powerful Daily Mail declared its judges “enemies of the people.” When the Supreme Court upheld the ruling, May was forced to take her proposed exit deal to the Commons. It was rejected three times, prompting her resignation.

Now, once again, the court has limited the powers of the prime minister. There is an echo here of the American conversation about impeaching Donald Trump. How should an established system deal with a populist politician who thrives on presenting himself as a man of action constantly undermined by outside forces? Trump is farther down this path: He clearly regards the normal constitutional safeguards as stifling and unfair restrictions on his personal power. To him, his interests and those of America are interchangeable. He is almost daring the rest of the political system to try to contain him, to give him an enemy to rail against. Johnson is pursuing a similar argument: First it was “the people versus Parliament,” and now it can be “the people versus unelected judges.”

There is a cascade of domestic consequences from the decision in Britain. First, it torpedoes a bad news cycle for the main opposition party, Labour, which has faced ridicule for the nebulous position on Brexit outlined at its party conference this week. Second, it means bills that were killed by the end of the parliamentary session have now been brought back to life. Third, it will allow the machinery of Parliament—such as select committees, urgent questions, and even speeches from the Commons floor—to be used to embarrass Johnson, not just over Brexit, but over an array of other stories, including allegations that he diverted public money to a close friend.

There are bigger implications, too. A sitting Parliament can make life harder for Johnson by pressuring him to bring back a new Brexit deal—or by forcing him to ask for an extension to the October 31 deadline. He has staked his political reputation on leaving the EU on that date “do or die,” but it is difficult to see how he can do so. Twenty-one of his own party defied him to vote to block a “no deal” exit, and there is little sign that he has a workable new deal ready.

All in all, the Supreme Court has handed a gift to the opposition, and turned up the heat on Johnson. Among Brexiteers, there have been suggestions that the court’s power is somehow illegitimate. Many of the senior figures in Johnson’s government are drawn from the Vote Leave campaign, which championed Brexit in 2016, and they have shown themselves willing to make populist arguments about the “will of the people.” With this ruling, Britain’s Supreme Court will be seen as stepping into politics in a similar fashion to its American counterpart. But unlike in the United States, Britain’s Supreme Court judges are appointed without political oversight, so there will again be whispers that “the establishment” is blocking Brexit, a measure backed by 52 percent of the voting population. In this worldview, the 2016 referendum result is a universal solvent for the awkward web of obligations that constrains the prime minister’s actions: to the remaining countries of the EU, to the Northern Irish peace process, to the sovereignty of Parliament.