The German Chancellor Angela Merkel, having just formed her fourth government, has established herself as one of Europe’s longest-serving leaders. But she enters her new term of office in a weakened position, and speculation has been turning to her possible successors.

In last year’s general election Merkel’s Christian Democratic Union (CDU) polled the lowest share of the vote in its history, and has remained in power only because its rivals are even weaker and unable to form a majority. Merkel has also come under fire from party colleagues for giving away too much ground on core policies during the months-long coalition talks with the minority Social Democrats (SPD).