and Jouke de Vries behind him by a 30% margin. In the January 2003 election, Bos entered a head-to-head race with incumbent Prime Minister and leader of the Christian Democratic CDA, Jan Peter Balkenende. Under Bos the vote and seats of the PvdA nearly doubled from 15% (23 seats) in 2002 to 27% (42 seats) in 2003. This resurgence was partially credited to Bos' charisma and youthful appearance (and according to some journalists Bos' "sexy touch"). Balkenende's CDA however remained largest the party by a margin of two seats. The ensuing coalition formation talks between Balkenende and Bos failed after several months. The CDA went on to form a government with the conservative liberal VVD, and the progressive liberal D66. At that time Bos was the leader of the largest opposition party. He spent considerable time reforming the PvdA's internal organisation and public image, together with the party's chairman Ruud Koole. He was criticized for his silence on important reforms and issues, and his moderacy which resulted in other parties claiming opposition leadership, among them most notably the Socialist Party. Although still enjoying large public support, criticism about his "style over substance" approach to politics was voiced in this period. At the December 2005 party congress, Bos announced that he aspired to become Prime Minister of the Netherlands, should the PvdA succeed in becoming the biggest party after the next parliament elections. And in the 2006 municipal elections, a few months later, the PvdA performed particularly well, becoming the largest party in local government. However, in the election campaign for the Dutch general elections of 2006 the PvdA – for the second time campaigning under his leadership – didn't manage to maintain this position as biggest party. Some considered pension reforms proposed by him to embattle the consequences of an aging population as a reason for this decline in popularity. Others emphasized a declining confidence in Bos among parts of the electorate that perceived him as "unreliable", as reason for this. Bos lost nine seats in the elections, which saw large gains for the main rival of Labour on the left side of the political spectrum, the more radical Socialist Party. Nonetheless, after these elections (and this time successful coalition talks with Prime Minister Balkenende), Bos became Deputy Prime Minister and Minister of Finance in the Fourth Balkenende cabinet, thereby breaking a campaign promise to only join a cabinet when