Has Donald Trump finally gone too far? So many people have asserted this so often in the past, with so little ensuing decline in his popularity, that the claim would seem to lack any hope of plausibility.

Yet there is reason to believe that Mr Trump really has gone too far and that this time even he realises it.

Future historians may trace his demise to the 12-minute tirade he delivered at a campaign rally in San Diego. That happens to be where a class-action lawsuit by unhappy graduates of the now-defunct Trump University is being heard. Mr Trump accused Gonzalo Curiel, the judge presiding over the litigation, of being “a hater of Donald Trump”, noting that the judge “happens to be, we believe, Mexican”. Mr Trump went on to describe the case as a “scam”, the federal court as a “rigged system”, and Judge Curiel as “totally biased” and a “total disgrace”. Challenged to explain himself later, Mr Trump responded, “I’m building a wall. It’s an inherent conflict of interest.”