Hillary Clinton’s campaign is not over, but the US presidential election in November seems ever more likely to be between Barack Obama and John McCain. It would be a fascinating struggle and a quite different one from the nomination contests seen up to now. The issue of personality, which dominated the Democratic race from the start, would not disappear – nor should it – but it would subside and leave space for an overdue debate about policy. This shift may test Mr Obama, if he is indeed the nominee, more than he and other Democrats expect.