Tuesday was a turning point on both sides of the Atlantic

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.