Who could take over as head of Germany's Social Democrats?

The 60-year-old leads a coalition of the SPD and the Christian Democrats in his northern state. In the Bundesrat — the council of Germany's 16 states and upper house of parliament — he serves on the Committee on Foreign Affairs and is deputy chairman of the Committee on European Affairs. Many in the SPD have long seen him as a possible new hope to lead the party forward.

Schwesig, born and raised in the former East Germany, is the first woman to lead the state of Mecklenburg-Western Pomerania. The 45-year-old previously served as minister of family affairs under Chancellor Angela Merkel, a role she used to push for equal opportunities for women and better state childcare facilities. She serves on the Bundesrat's Committee on Foreign Affairs.

Scholz, 60, is seen by some of his fellow party members as a technocrat and is considered to belong to the SPD's conservative wing. As finance minister under Merkel, he has been committed to curbing public spending and keeping a lid on new debt. He also served as federal minister of labor and social affairs in Merkel's Cabinet from 2007 to 2009.

A reasonably popular figure in the SPD, Dreyer was voted in as deputy party chairwoman in 2017 with 97.5% backing. Despite repeatedly stating she would not want to leave her western state for Berlin, she is still seen as a possible replacement for Nahles. The 58-year-old has served as premier of Rhineland-Palatinate since 2013 and is the first woman to hold the office.

The 59-year-old Bundestag member from Cologne is one of the deputy chairs of the SPD's parliamentary group. In that role, he is responsible for foreign affairs, defense and human rights policy. He is well respected within the party and could be tapped as interim SPD leader in the Bundestag.

The 60-year-old sociologist leads the SPD in Germany's most populous state, North Rhine-Westphalia. He is a deputy chair of the SPD's parliamentary group, overseeing budgetary affairs, finance and Europe. As secretary-general of the Party of European Socialists, he is also considered well connected at the European level.

The former president of the European Parliament has been suggested as another possible challenger. The 63-year-old ran as the SPD's candidate for chancellor in 2017 but lost to Merkel. He subsequently stepped down as SPD leader. He has already said he doesn't want the job back, but Germany's Bild am Sonntag newspaper reported last week that he was keen to lead the SPD parliamentary group.