When Governor Eliot Spitzer of New York offered, in late September, an “administrative policy change” that would have enabled illegal aliens to apply for state drivers’ licences, he set off a furious revving of political engines that has still not quietened down.

The licences-for-aliens issue hasn’t just provided fodder for gleeful tabloids out to embarrass Spitzer (dubbed “Gov. Flipser” after he retracted his plan once he’d gauged how unpopular it was). It has vaulted, also, into the debates between the Democratic presidential candidates, as well as into the wider national punch-up on the subject of immigration reform.