When the history of this era is written, Tuesday, Sept. 24, 2019, will be remembered as the day when venerable Anglo-American democratic institutions fought back against Anglo-American leaders who sought to undermine them.

In the morning, the British Supreme Court ruled that Prime Minister Boris Johnson cannot, after all, suspend Parliament to push the United Kingdom out of the European Union without any trade deal or treaty. The ruling was modest, as some have argued, because it did not suggest a punishment or remedy: The court declared, simply, that Parliament is still in session.

In the evening, on the other side of the Atlantic, House Speaker Nancy Pelosi, D-Calif., finally snapped and called for impeachment hearings. There is an immediate cause: President Donald Trump allegedly asked his Ukrainian counterpart to fabricate a legal case against former vice president Joe Biden and used a promise of U.S. military aid to blackmail the Ukrainian leader into agreeing. But there is a deeper backdrop, too. The House has also been frustrated for months by the White House’s unconstitutional refusal to produce witnesses and evidence, thus making it impossible for Congress to conduct any form of meaningful oversight, and by Trump’s continued defiance of legal and behavioral norms. By contrast with Britain, impeachment hearings will not be modest or quiet. Expect months of raucous political debate.

There are many other differences between the British and the American stories, too numerous and mostly too obvious to list here. But there is one similarity: In both countries, the future of elected legislative bodies now weighs in the balance. Both the British Parliament and U.S. Congress have, in recent years, lost significance, popularity and even legitimacy as their respective executive branches took more and more prestige and power. Increasingly, both legislative bodies are seen as divisive, argumentative and inefficient — and not without reason. Congressional polarization has made it difficult to pass even the basic laws needed to keep the government running. Parliamentary divisions have made it impossible either to choose any sensible form of Brexit or to reverse Brexit altogether. In both countries, real political debate has shifted away from the House of Commons and the Capitol, and toward television studios and social media.

Now the Supreme Court in Britain and the speaker in the United States, have reasserted the right of legislators to write the political script and control political events. But with this reassertion comes an enormous responsibility. The British Parliament, now that it has been reconvened, must come up with a clear solution, either for a sensible Brexit or against it. If it does not, then Parliament’s reputation might never recover. Congress, likewise, must make a clear case for impeachment, one that at least convinces the majority of Americans and at best persuades the Senate to follow along, too. If hearings are frivolous, or overly partisan, or badly organized; if members use the opportunity to grandstand; if the evidence is insufficient or unimpressive then the prestige of Congress, and especially of the Democrats in Congress, will not recover either. And then we are in a different era in which presidents and prime ministers have, in practice, unlimited power.

“The good of the people is the supreme law,” wrote Cicero, the statesman and orator who fought against the end of the Roman Republic. But who gets to decide what is the “good of the people”? That’s what’s at stake on both sides of the Atlantic.

Washington Post columnist Anne Applebaum is a Pulitzer Prize-winning historian and a professor of practice at the London School of Economics.