As British Prime Minister Keir Starmer faces calls to resign for his appointment of Epstein-tied Peter Mandelson as ambassador to the United States, one is struck by the sudden instability of British governments. In the 28 years between 1979 and 2007, Britain had only three prime ministers, while in the 19 years since 2007, it has had seven, and may soon have eight. Only one of those, David Cameron, carried his party to a re-election victory, and he resigned a year after being beaten in the Brexit referendum.

It’s not just leaders who have stumbled. Even historically long-lasting parties have. Britain’s Conservatives, who, since the party’s founding in 1846, 180 years ago, have been the most electorally successful party anywhere, are polling at 19% today.

Similarly, elsewhere in Europe, France’s historic socialist, communist and Gaullist parties have more or less disappeared, and the National Rally, dismissed as unthinkable, to the point that the judicial establishment disqualified it from the ballot, still leads the polls under its 30-year-old successor.

The two American political parties, the oldest and third-oldest in the world, have shown more stability. In the first half of the 20th century, Democrats survived the landslide rejection of Woodrow Wilson in 1920, and Republicans survived the landslide rejection of Herbert Hoover in 1932.

Now, a century after Word War I, immigration is the problem that, more than anything else, is threatening the hold of longstanding political parties. Old parties’ leaders in Britain and Europe, nervous that below-replacement birth rates would halt economic growth and endanger their welfare states, encouraged massive immigration of Muslims from North Africa, the Middle East and Pakistan. Prime example: former German Chancellor Angela Merkel’s unilateral decision, without consultation internally or with European Union partners, in 2015 to admit 1 million mostly male Muslims to Germany.

Police authorities and established journalists suppressed evidence that many migrants lived off welfare rather than productive labor, and that many such men felt justified in raping headscarf-less young women and beating up gay men.

Authorities seemed to regard any qualms about immigrants with unfamiliar customs as equivalent to the bigotry that fed the Holocaust and ignored the obvious moral difference between excluding people from your country and murdering your fellow citizens.

Whether Starmer survives politically is unclear, but it is clear that the Labour Party, like the Conservatives before it, is in perhaps terminal trouble.

The situation in America, and concerning its parties, is less drastic. The nation has a much stronger tradition of assimilation of immigrants, although many American liberals regard that as something like persecution. And our great immigration surge between 1982 and 2007 came primarily from Latin America and Asia.

Nonetheless, immigration has affected our politics, and the Clinton Democrats’ and Bush Republicans’ implicit acquiescence in the 1982-2007 surge are things of the past. Even though immigration was reduced sharply by the 2007-08 financial crisis and the illegal immigrant population plateaued thereafter, President Donald Trump’s border-strengthening efforts in his first and second terms have made the Republicans a skeptical-of-immigration party.

Democrats have also changed in response to Trump. Former Presidents Bill Clinton and Barack Obama proclaimed that they were enforcing immigration laws. Former President Joe Biden scarcely bothered, even as his appointees put in place an open-borders policy. Today, most Democratic officeholders are intent on obstructing and, in the tradition of Democrats John C. Calhoun and George C. Wallace, nullifying federal law enforcement.

On both sides of the Atlantic, we are seeing in the 2020s something like reenactments of the 1920s — the overthrowing of political establishments in Britain and Europe, and the sometimes awkward and painful reshaping, but not overthrowing, of the political parties of the U.S.