Minister-President of Schleswig-Holstein, 2005–2012
Carstensen was the CDU's candidate for premier of Schleswig-Holstein in the state election of 20 February 2005; he led the CDU to its best result since Uwe Barschel’s resignation in 1987 with 40.2% of all votes cast, making the CDU the strongest party in the state parliament for the first time since 1983. However, the coalition of the CDU and the Free Democratic Party (FDP) failed to obtain a majority by some 700 votes. The Social Democrat (SPD) office-holder Heide Simonis thus tried to form a minority cabinet of the SPD and Bündnis '90/Die Grünen (the Green party) tolerated by the Danish minority party SSW.
From 1 March to 27 April 2005 Carstensen was leader of the CDU in the state parliament.
In the vote to decide the premier of Schleswig-Holstein in the opening session of the state parliament on 17 March 2005 incumbent Heide Simonis (SPD) did not receive the required majority. Subsequently successful negotiations between the SPD and CDU led to the formation of a grand coalition between SPD and CDU. On 27 April 2005 Carstensen was finally elected premier of the state of Schleswig-Holstein with a majority of 54 votes (out of the grand coalition’s 59).
In February 2009, Carstensen and Mayor Ole von Beust of Hamburg agreed on a €13 billion bailout of state-owned shipping financier HSH Nordbank. The two states were forced to intervene after the SoFFin fund, which had been set up by the federal government in 2008 to stabilize the financial markets, said it could not help out HSH Nordbank until it got rid of all its bad debts.
In July 2009 Carstensen announced that he would seek early state elections as a result of ongoing quarrels within the coalition government. After the Elections of 27 September 2009 Carstensen was reelected on 27 October 2009.
During his time as Minister-President, Carstensen also served as President of the Bundesrat, Germany's upper house of parliament. He served as a CDU delegate to the Federal Convention for the purpose of electing the President of Germany in 2010 and 2012.
