PvdA, or 'Dutch Labour' went into opposition for the first time since 1989, when the party formed a coalition with the Christian Democrats (CDA) and PvdA party leader Wim Kok became Minister of Finance. In 1994 he became prime minister in a PvdA-VVD-D66 cabinet (Kok-I), then without CDA.
When the 1st Balkenende cabinet exploded due to political inexperience of LPF (the new Fortuyn Party that gained the seats that PvdA lost in May 2002) Bos challenged Jan Peter Balkenende. In the new elections of January 2003, Bos nearly became leader of the biggest party, as the PvdA regained much of the seats lost in the May 2002 elections. Balkenende and the CDA got 44 seats and the PvdA got 42 seats thanks to the charismatic leader Bos. From 1st party due to Kok and 4th party due to Melkert, the PvdA became 2nd, and even close to 1st again, due to Bos. He has been named the 'leftwing answer to Pim Fortuyn'.
But Bos did not succeed in forming a coalition government CDA-PvdA. The CDA, after first trying with Bos, preferred a coalition with VVD and instead of LPF, this time with D66. Now Bos is opposition leader in the Dutch parliament, although his moderacy some times gives lead to other parties claiming opposition leadership. The socialist Jan Marijnissen of the much smaller Socialist Party (SP) is called 'opposition leader' as well.
In the Netherlands, he is brilliantly portrayed in the satyrical programme Kopspijkers.