Although denied the Democratic nomination for the presidency, Bernie Sanders is a man who, seemingly, never gives up. Usually an admirable quality in a politician, Mr Sanders seems to be pursuing his late-blossoming career (he is 74, and would be 83 by the end of a putative two-term presidency), perhaps a little too hard now.

For he is at risk of damaging Hillary Clinton’s chances so badly that he allows Donald Trump to win the presidency, and certainly more easily than The Donald deserves. Mr Sanders could inadvertently achieve this do this either by simply refusing to support Mrs Clintons bid, or to do so in an obviously dog-in-the-manger fashion; or, a possibility increasingly mooted, by running himself as an independent. One wonders if Mr Sanders is so sweetly deluded that he thinks he could push his two mainstream rivals out of the way from the red-green left. The form book suggests that would be a foolish move.

Not a few of America’s 43 presidents owed their time in office to the intervention of a brave but ultimately quixotic third party candidate. There is at least a case that the near 100,000 votes for Ralph Nader in the state of Florida in the 2000 contest, famously won by a few hanging chads that fell George W Bush’s way, robbed Al Gore of the White House. It also, more to the point, deprived the world of a more statesmanlike approach to the problems of 9/11, the Taliban, Al- Qaeda and Saddam Hussein.

Further back, Jimmy Carter's prospect of a second term were done no good by the candidacy of the near-forgotten centrist Congressman John Anderson; much the same could be said of Ross Perot's pitch in 1992, which edged Bill Clinton ahead of George HW Bush. In a more complicated way George Wallace’s racist campaign helped Richard Nixon in another close contest in 1968; and there are other examples stretching back to the days of Teddy Roosevelt, Woodrow Wilson and beyond.