Donald Trump was a teenager when Lyndon Johnson, the 36th US president, signed the bill that helped him become the 45th. The 1965 Immigration and Nationality Act gets lost in the lore of the 1960s, but few events outside war and the Depression have done more to change America.

By ending the preference for European immigrants, the law expanded the US population over time and made it enormously less white. It also led to the build-up of ethnic angst that broke through half a century later. The election of Mr Trump in 2016 was above all a howl against demographic upheaval.

His growing chances of defeat this year reflect the easing of that angst. Among the reasons for Mr Trump’s polling woes — the bungling of the coronavirus pandemic, the shrewdness of his Democratic challenger Joe Biden — one of the least examined is the collapse of immigration as a political issue. The subject on which Mr Trump defined himself against the Republican establishment, and then Democrat Hillary Clinton, has gone mostly undiscussed in this otherwise raucous election.