On the surface, Donald Trump’s escalated race-baiting looks self-destructive. The US economy is growing. Middle-class wages have been picking up. Mr Trump’s re-election aim should be to broaden his base to include non-whites — or at least reassure moderate white voters who are queasy about reliving the US civil war. Yet he is steaming in the opposite direction. Telling US-born Democrats to go back to the countries they came from is a departure even by Mr Trump’s standards. In 2016, he attacked immigrants, chiefly Muslim and Mexican, as a threat to national security. Now he is portraying opinionated non-whitecitizens as un-American. Their citizenship is performance-based.

To Mr Trump, whites are automatically American. Others only qualify if they support his idea of what it is to be American. By any measure, this is textbook racism.

But there is method behind Mr Trump’s nastiness. His goal is to force Democrats to unite behind the so-called “Squad” of four non-white congresswomen, whose radicalism is not popular in the US heartlands. Most Americans are not socialist. Nor do they support paying reparations for slavery, or open borders. Most would probably be suspicious of a Green New Deal that aimed to abolish fossil fuels by 2030. These are the kinds of radical ideas Mr Trump wants to force Democrats to support. The more repulsive his attacks on the four women — led by Alexandria Ocasio-Cortez, who, like two of the others is US-born — the more he compels Democratic presidential candidates and the US media to rally behind them. That, in Mr Trump’s view, is his ticket to a second term.