The time has come for Hillary Clinton to make a historic announcement, certain to dismay her friends and confound her enemies, demonstrating her undeniable strengths – intelligence, ambition and resolve. Following on her massive Wisconsin primary defeat, she ought to surprise the nation and the world by announcing her decision not to contest Texas, Ohio or Pennsylvania, accepting Barack Obama as the Democratic presidential nominee in opposition to John McCain.

Though she has been intermittently hostile in her comments on Mr Obama, it should be possible for her to say that she will do whatever she can to prevent a Republican victory in November. She needs to represent her withdrawal not as a personal sacrifice, but as a refusal to play the Republican game that could lead to a McCain victory and the elevation of justices to the US Supreme Court hostile to her most cherished values. The time has come to say that Republican rule, as exemplified by the Bush administration and McCain pledges, offer prospects too dangerous to contemplate.