There comes a time in US primary campaigns when a leading candidate starts to act presidentially rather than as a candidate looking for party nomination. In the current Democratic campaign, the longest on record, Hillary Clinton has already made that shift, much to the resentment of her rival candidates.
Their hopes of reversing her lead after this week's sharp debate in Philadelphia were obscured by further polling evidence yesterday that she still enjoys a strong lead over any likely Republican opponents in most states and among many categories of voter.
Mrs Clinton was certainly put on the defensive in this encounter by a sustained attack from the other Democratic candidates. They criticised her for political opportunism and inconsistency on Iran, Iraq, pension reform, free trade, illegal immigrants driving taxis in New York and on presidential secrecy. She is convinced it is necessary to appeal beyond her party to potential swing voters at this stage in order to consolidate her position, while they hope to upset her confident lead. By concentrating on these issues Barack Obama and John Edwards landed several rhetorical blows, although Mrs Clinton fought back tenaciously.
She remains a uniquely polarising figure in US politics. This leads many analysts to conclude she is the Democratic candidate who would best rally the Republican base - and is therefore unelectable against it. Her defenders say she is well able to respond in kind to the barrage of negative campaigning Republicans would throw at her, not least because of her experience of Bill Clinton's famed ability on that score. By being so hawkish at this stage she fends off accusations of being weak on national security. And swing voters aware of how much the US has lost its reputation and influence around the world may support her because with her husband's help she could credibly claim an ability to retrieve it.
But this is still an open contest for the Democratic candidacy. The Iowa primary on January 3rd remains a close call between these three, with huge implications for their subsequent campaigns as they move to New Hampshire and beyond. There remains much scope for mistakes, misjudgments and upsets. Indeed avoiding them in the next few months will be a gruelling test of her mettle and endurance. By switching to presidential mode so soon she pitches herself against the more radical party base. Her ruthless journey towards the centre, accompanied by an unscrupulous triangulation of policy positions, strikes many Democratic activists as a step too far too soon. She must now manage that current perception against her search for electability next November.