Kramp-Karrenbauer (since 2018). On 7 June 2011, he was among the guests invited to the state dinner hosted by President Barack Obama in honor of Chancellor Angela Merkel at the White House. Under Bouffier's leadership, Hesse joined forces with Bavaria in early 2013 to launch a constitutional challenge to the Germany's system of tax transfers in order to stop subsidising spending in the city of Berlin, the national capital, and all the poorer states. At the time, Hesse was the third largest net contributor, with an annual transfer of almost €1.3 billion. On 8 February 2013, Bouffier agreed to the proposal of the President Joachim Gauck to hold the state elections on the same day as Germany's federal elections. When the official result gave no major parties and their traditional coalition partners a clear majority in the parliament, Bouffier decided to break ranks with the rest of Chancellor Angela Merkel's conservative party and seek a coalition government with the Greens rather than the Social Democrats (SPD). He thereby created only the second CDU-Green coalition to govern a German state, after the previous government of Hamburg. On the federal level, he was part of the 15-member leadership circle chaired by Merkel, Horst Seehofer and Sigmar Gabriel in the negotiations to form a coalition government. As one of the state's representatives at the Bundesrat, Germany's upper house of parliament, Bouffier is a member of the Committee on Foreign Affairs and the Committee on Defence. In October 2015, while he held the rotating presidency of the Bundesrat, he hosted the three-day festivities for the 25th anniversary of the reunification of the former East and West German states. On 25 February 2022, Bouffier announced his resignation from the post of minister-president which will become effective on 31 May. Other activities Corporate boards Helaba, Member of the Board of Public Owners (2010–2022) KfW, Member of Board of Supervisory Directors (2011-2013) Non-profit organizations Committee for the preparation of the Reformation anniversary 2017, ex-officio member of the board of trustees Deutsches Museum, member of the board of trustees Hessische Kulturstiftung, chairman of the board of trustees (2010–2022) House of Finance at the Goethe University Frankfurt, member of the board of trustees Paul Ehrlich Foundation of the Goethe University Frankfurt, honorary chairman of the board of trustees Senckenberg Nature Research Society, chairman of the board of trustees Stiftung Deutsche Sporthilfe, member of the board of trustees Landesstiftung Miteinander