This paper examines Tony Blair’s use and loss of leadership capital between January and May 2005. Despite concern that Blair had earlier ‘squandered’ his authority, according to the Leadership Capital Index (LCI) Blair still possessed a series of advantages that gave him ‘capital’ to ‘spend’. This included his personal skills, eight years’ experience in office and, crucially, a continued polling lead and huge parliamentary majority. So why in this period did Blair achieve so little and appear so beleaguered? The LCI demonstrates how these attributes proved superficial. The ‘credit’ parts of the LCI were waning and isolated while the ‘debit’ parts fed off each other as a continuously eroding cycle. While his skills remained, Blair’s relations and reputation were eroded: the presence of a serious rival in Gordon Brown, party rebellion and increasing loss of trust over Iraq worked together to reduce and erode any leadership capital his advantages could bring. Moreover, these factors reinforced each other in a negative cycle. We place leadership capital and Blair’s premiership within the context of ever shifting academic debate on prime ministerial power in the British political system.