As the contest for the US Democratic nomination has dragged on, supporters of Barack Obama have called on Hillary Clinton to drop out. She can no longer hope to win, they say, and the rivals’ bitter fight now serves only to hurt the Democrats’ prospects in November. While they pound each other’s weaknesses and question each other’s integrity, John McCain can concentrate on raising money for the general election and uniting Republicans round his candidacy. For the good of her party and the country, she keeps being told, Mrs Clinton should quit.

This is wrong. Mrs Clinton’s chances of winning the nomination are poor, it is true, but this race is not yet over. Mr Obama has a lead in pledged delegates (awarded, by complex formula, on the basis of votes cast in the primaries and caucuses), and will almost certainly still have it by the end.