Donald Trump cannot become President of the United States.  He will be shunned by its black, Hispanic, Asian and other ethnic minority members, who make up about a third of eligible voters.  He is already an anathema not only to its women voters, but even to many Republican women voters: one poll found that almost half of them can’t see themselves voting for him.  He cannot win enough of the states with the biggest electoral college votes, most of which voted Democrat in 2012 – such as California, New York, Pennsylvania, Illinois.  All in all, his candidacy is reinforcing the Republicans’ weakness in Presidential contests with knobs on.

To make this case is essentially to argue that the usual rules of these elections will apply next autumn.  That sounds right.  But, then again, that the usual rules of Republican presidential primaries would apply sounded right, too – and Trump broke them.  This is making some of the commentators who previously wrote him off as a loser very nervous indeed.

Furthermore, Hillary Clinton’s current popularity ratings are not much better than her opponent’s.  Only one in three American voters have a favourable view of him.  When her own standing is tested, that proportion rises to the dizzy heights of two in five.  Bernie Sanders is wreaking the same sort of damage on her in the Democratic primaries that Trump’s opponents inflicted on him in the Republican ones.

But the most formidable obstacle between Clinton and the White House may turn out to be neither Saunders nor Trump – nor even the detestation that very many Americans have for her and her husband.  What happens if, after her adoption as the Democrats’ candidate, the FBI moves to indict her over allegations about the uses of her private e-mail system – in other words, that laws were broken when and after government information was sent to it?  What happens if she is charged with destroying classified government information, and could consequently be sent to jail?  The Democrats could not run a candidate for President who had a possible prison sentence hanging over her head.

Furthermore, it is not inevitable that her Vice-Presidential pick would step up to take her place.  But since her or she might well in such a circumstance, none the less, there is a new and special reason this year for paying attention to her choice.  It is possible that the next President of the United States will be neither Trump nor Clinton but rather……….