Hillary Clinton’s campaign for the presidency refuses to quit. Tuesday’s Pennsylvania primary showed, moreover, that her remarkable tenacity is matched or even exceeded by her supporters’ determination to see that she is not bounced out of this race. Her roughly 10-point win was too little to derail Barack Obama, or to change the arithmetic of pledged delegates that is securely in his favour. But it breathes some life into the argument Mrs Clinton is putting to the Democratic party’s unelected “super-delegates”, who in the end will choose the winner.

Once again, she and her supporters say, Mr Obama should have clinched the thing, and failed to. He outspent her in the state by a huge margin (something he will also be able to do in the remaining primaries) yet still could not win. Despite recent gaffes and embarrassments, he halved the lead Mrs Clinton once enjoyed in the state, but her majorities among key Democratic constituencies – the white working-class, women, the elderly, the relatively uneducated – were as solid as ever.