Tony Blair’s first visit outside London after his election landslide in May 1997 was to the Royal Ulster Agricultural Show in Balmoral, near Belfast. Among the prize bulls, he tried to reassure unionists that they were safe under a Labour government, and in his speech he said: ‘“None of us in this hall today, even the youngest, is likely to see Northern Ireland as anything but a part of the United Kingdom.” It worked. Now, after Boris Johnson’s Brexit deal, the unionists can no longer be so sure.