Large countries nurse an insecurity of their own. Their size promises power but their endless borders gift the outside world opportunities for incursion. The resulting spirit - half-brash, half-fearful - marks the politics of Australia, Russia and, most vividly right now, the United States. Its southern frontier is the nearest thing to geographic bad luck in a land otherwise screened from the world's troubles by oceanic distance.

It is this deep-set fear that drives a government to prise illegal immigrants from their blameless offspring. None of the merely political motives attributed to President Donald Trump add up. As a campaign theme for November's mid-term elections, immigration distracts from the Republicans' preferred focus on the strong economy. Footage of confused children in foil bed sheets has roused the distaste of most voters. If this was a Beltway ruse to force Democrats to give Mr Trump his wall on the Mexican border, then it was a ruse that Republican legislators - such as South Carolina Senator Lindsey Graham - were not in on.